30"+ work space low cost diy CNC router parts kits?

[wizard]

You've given me some ideas to work with. You also reminded me that there is a bunch of contractors supply stores near where I live. I haven't been into any of them before because they are more for commercial use but now would be a good time to see if they have anything good for this purpose.

The biggest problem with stores targeting contractors is some don't want to work with people without a tax number. That is they are business to business and will actually turn away somebody walking in off the street looking for parts. Around here most electrical supply houses are open to the public. However Graingers at one time wouldn't and some of the HVAC supplier won't work with nonbusiness entities.

It is a real pain, America is turning into a country where if you aren't a professional you don't have access, sort of like the guilds of the Middle Ages. I grew up in farm country where the owners had to wear many hats to get the job done at the end of the day. It is a bit offensive to say you can't do business with us because you aren't a member of our approved customer list.

In any event I would highly suggest that you know what you want before going into a supply house for contractors. The thing is they generally don't want to waste time with people that have to be guided through the purchase. The other thing is that when you arrive a will call desk or service counter you see very little of what they have in stock. So if you want a specific bracket you better know what the manufactures name is, their (manufactures) part number and any other information that might be needed to pick the order. Generally you won't be walking the aisles.

I wish I had your instinct to stay away from the open builds store. Believe me, I also have a hard time trashing stuff I paid for but there is no way I can rely on their parts to keep my frame rigid. They can't even keep themselves rigid. I need L brackets with no visible flex. Their stuff bends like paper clips and that is not one word of exaggeration. They are quite literally and precisely that bad.

Much of this comes from working in industry since I left high school in the very late 1970's. Somethings just rub you the wrong way even on machines that are being built for low costs. This is why I don't dismiss wood for a low end router build, it actually can be justified over some of the other solutions I've seen. Wood in this case being a good grade laminated material.

The Open Builds stuff has overtaken my Betamax video player and Wild Wild West DVD as my worst purchase of all time and I have a solar power flashlight!

Hey now; a solar powered flashlight, assuming it charges a battery, is actually a good idea. Sadly many of the implementations out there suck badly. Given that I'd buy one in a heart beat if it passed my robustness sniff test.

[ger21]

It is a real pain, America is turning into a country where if you aren't a professional you don't have access,

I would argue that these businesses have always been this way. If anything, things are actually moving in the other direction, especially with the internet. You can easily buy stuff today that would have been almost impossible to find 10 years ago.

[louieatienza]

You've given me some ideas to work with. You also reminded me that there is a bunch of contractors supply stores near where I live. I haven't been into any of them before because they are more for commercial use but now would be a good time to see if they have anything good for this purpose.

I wish I had your instinct to stay away from the open builds store. Believe me, I also have a hard time trashing stuff I paid for but there is no way I can rely on their parts to keep my frame rigid. They can't even keep themselves rigid. I need L brackets with no visible flex. Their stuff bends like paper clips and that is not one word of exaggeration. They are quite literally and precisely that bad.

The Open Builds stuff has overtaken my Betamax video player and Wild Wild West DVD as my worst purchase of all time and I have a solar power flashlight!

The OpenBuilds stuff is what it is... Low cost automation stuff for newcomers to DIY CNC. There's some nice builds there. But to me it's somewhat of a throwback to the days when v-bearings were the thing in the DIY CNC world (MechMate, Joe's 4X4, etc...) Profile rails and ballscrews was easy to get if you knew how to look and decipher a company's product code (I studied THK, NSK, and Kuroda catalogs like I was going in for a test back then!) Linear actuators could be found for under $100. Now everyone on eBay thinks they found gold and charge as such. Deals don't come around as much. But some Chinese companies are putting out good quality profile rail for not much more than what supported round rail went for not long ago (HiWin, PMI, TBI, HSAC, etc...) AutomationTechnologies actually have some decently priced sets I wish were around back when I first started off.

McMaster Carr ships out of New Jersey. I get parts in one day. Cost a bit more, but I get them fast.

I would argue that these businesses have always been this way. If anything, things are actually moving in the other direction, especially with the internet. You can easily buy stuff today that would have been almost impossible to find 10 years ago.

Definitely. I get stuff from THK and Misumi and Lin Engineering, no problem. I've spoken with engineers at Parker and Kollmorgen, and they've been kind to answer my questions. Kuroda on the other hand, don't want to know me. The amount of vendors on Aliexpress you can deal with directly, for example, is mind-boggling. There are tons of great deals in the automation surplus warehouses, if you know what to look for.

[Goemon]

I've always thought of Aliexpress as the spiritual home of the Internet scammer. One of my other hobbies is air guns and a lot of people buy high pressure Chinese compressors off that site but I have never been brave enough.

Apparently if you use a prepaid credit card, the risk is not too bad.

My views on ordering from Chinese vendors has been colored a little by the overwhelmingly negative experiences I have had in the past - vendors from there always seem to tell me what I want to hear and then send me something that is well below my expectations.

My expectations are probably the problem. I think that a good deal is when you get the same quality for less money. If someone sends me a lower quality product for less money, I don't consider it cheap. I just expect silver to cost less than gold. I usually feel ripped off and regretful with anything I have ordered from China.

I have ordered a lot of stuff from McMaster Carr and I agree 100% that they are a top quality outfit. Never had an issue and they always exceeded my expectations on delivery times and service. They aren't exactly cheap though.

I think I got a good deal on my THK rails off eBay. I bought used ones but I know so little about rails that I have no clue if I really did well. They all seem very sturdy and well made. The bearing slide smoothly but I don't know what else to look for.

[Goemon]

I'm a little stuck on my motor cables and this resistor thing. Apparently most of the pre-made Gecko G540 motor cables do no come with the resistors which makes them pointless to me.

I already have a bunch of regular db9 cables and breakout boards from my arcade building days. I can solder a cable if I have to but I am not very good at it. My homemade cables were usually a source of problems for me when I build diy arcade machines so I was hoping to buy plug in and play cables for my CNC build.

Does anyone know of any gecko g540 cables that come with the resistors built in? If not, how do I know which ones to choose for my 381oz Nema 23 motors (from Automation Technologies)?

Do the resistors need to be shielded or could I just slot them into my db9 breakout boards with the wire ends twisted around the other side? I am dreading the idea of using my soldering iron again....

[louieatienza]

I've always thought of Aliexpress as the spiritual home of the Internet scammer. One of my other hobbies is air guns and a lot of people buy high pressure Chinese compressors off that site but I have never been brave enough.

Apparently if you use a prepaid credit card, the risk is not too bad.

My views on ordering from Chinese vendors has been colored a little by the overwhelmingly negative experiences I have had in the past - vendors from there always seem to tell me what I want to hear and then send me something that is well below my expectations.

My expectations are probably the problem. I think that a good deal is when you get the same quality for less money. If someone sends me a lower quality product for less money, I don't consider it cheap. I just expect silver to cost less than gold. I usually feel ripped off and regretful with anything I have ordered from China.

I have ordered a lot of stuff from McMaster Carr and I agree 100% that they are a top quality outfit. Never had an issue and they always exceeded my expectations on delivery times and service. They aren't exactly cheap though.

I think I got a good deal on my THK rails off eBay. I bought used ones but I know so little about rails that I have no clue if I really did well. They all seem very sturdy and well made. The bearing slide smoothly but I don't know what else to look for.

Automation components one of the few things whereyou get what you paid for, generally. Whether you can utilize thefeatures is another.

You can get THK with either interchangeable or matched blocks. If they're matched, the master set will have serial on the rail and blocks, and the master rail will have a groove on the bottom. The s/n on all parts should be oriented the same way, and the edges closestto the s/n are the datum surfaces... Also, some sets, SR, RSR, do not have retained bearing balls, and they'll fall off if you slide the blocks off the rail. They're also designed for horizontal mounting, while HSR and SHS can be mounted in any direction. There are more types but these are the most common...

[jpvonoy]

The resistor values need to be matched to the current draw of the motors you are using which is probably the reason they aren't built into most cables. I soldered my resistors into the backshell of the db9 connectors at the g540 end of the cables. I also made my own cables using 18 ga wires.

My first attempt was to use standard db9 cables but the wires were too small and they overheated the drivers and the wires got really hot, shutting down the g540 after about 15 mins of operation. So make sure if you buy premade cables that they use a heavy enough gauge of wire. For your motors 18 ga is prob required. Without doing the calculations, if the cables are more than 10 feet or so in length you may want 16 ga.

Sent from my Nexus 6P using Tapatalk

[louieatienza]

I'm a little stuck on my motor cables and this resistor thing. Apparently most of the pre-made Gecko G540 motor cables do no come with the resistors which makes them pointless to me.

I already have a bunch of regular db9 cables and breakout boards from my arcade building days. I can solder a cable if I have to but I am not very good at it. My homemade cables were usually a source of problems for me when I build diy arcade machines so I was hoping to buy plug in and play cables for my CNC build.

Does anyone know of any gecko g540 cables that come with the resistors built in? If not, how do I know which ones to choose for my 381oz Nema 23 motors (from Automation Technologies)?

Do the resistors need to be shielded or could I just slot them into my db9 breakout boards with the wire ends twisted around the other side? I am dreading the idea of using my soldering iron again....

CNC Router Parts sells them, but you have to see if they match up with the rated current on your steppers. You only need to solder pins 5-9, and bridge the resistor on pins 1 and 5. Soigeneris makes a DB9 breakout board with asjustable resistor that fits in DB9 cover..

You don't necessarily need the resistor unless your motors are rated less than 3.5A, but you'll deactivate idle current reduction...

[wizard]

I would argue that these businesses have always been this way. If anything, things are actually moving in the other direction, especially with the internet. You can easily buy stuff today that would have been almost impossible to find 10 years ago.

This is likely true but i think it varies some with location. It can be frustrating though, i spent years working on a variety of industrial furnace in the foundry i worked at. I could have parts in a day sometimes hours and that was going through the purchasing department. Now it is a chore to get parts for the old furnace in my cellar. This just rubs me the wrong way.

As for automation parts i suspect part of the issue here is the explosion of suppliers over the last couple of decades. The competition means that the old ways if getting product sold no longer apply. One no longer has to deal with an old line electrical supplier for things like servos and steepers. I think it is fair to say we have hundreds of companies supplying such parts now. These companies can't break into old distribution channels so are forced to find alternative ways to sell stuff.

[louieatienza]

This is likely true but i think it varies some with location. It can be frustrating though, i spent years working on a variety of industrial furnace in the foundry i worked at. I could have parts in a day sometimes hours and that was going through the purchasing department. Now it is a chore to get parts for the old furnace in my cellar. This just rubs me the wrong way.

As for automation parts i suspect part of the issue here is the explosion of suppliers over the last couple of decades. The competition means that the old ways if getting product sold no longer apply. One no longer has to deal with an old line electrical supplier for things like servos and steepers. I think it is fair to say we have hundreds of companies supplying such parts now. These companies can't break into old distribution channels so are forced to find alternative ways to sell stuff.

That's because the oil company wants you to get into their service plan. Follow the money!

[ger21]

Now it is a chore to get parts for the old furnace in my cellar.

I recently bought parts for my furnace, from Amazon, and had them the next day for $10 shipping.

[wizard]

You are very kind with respect to OpenBuilds. Im far more inclined to point people in a different direction.


As far as industrial suppliers like THK and Misuni being more open when it come to individuals there are many factors. One that is probably very real is that it is no longer considered to be weird to have a CNC machine in one cellar, garage or even the bedroom. OK maybe you are still weird if the machine is in the bedroom. I know back in my younger years, the 1960's through the 1980's it would have been strange to run into someone with a CNC machine in a home shop. If they did have such a machine you would assume that they where filthy rich. Now the opinion of such people would be cool followed by question like what do you do with it.

So i suspect manufacture are just acknowledging the fact that DIY CNC has enough volume for them to take an interest. Then you have the reality of retired CNC machines leaving industry and sometimes ending up in home shops. The incentive is there to supply these users as they are no longer weird.

The OpenBuilds stuff is what it is... Low cost automation stuff for newcomers to DIY CNC. There's some nice builds there. But to me it's somewhat of a throwback to the days when v-bearings were the thing in the DIY CNC world (MechMate, Joe's 4X4, etc...) Profile rails and ballscrews was easy to get if you knew how to look and decipher a company's product code (I studied THK, NSK, and Kuroda catalogs like I was going in for a test back then!) Linear actuators could be found for under $100. Now everyone on eBay thinks they found gold and charge as such. Deals don't come around as much. But some Chinese companies are putting out good quality profile rail for not much more than what supported round rail went for not long ago (HiWin, PMI, TBI, HSAC, etc...) AutomationTechnologies actually have some decently priced sets I wish were around back when I first started off.

E-Bay has become really terrible, it is almost a suppler of last resort. You can still get lucky but for the most part bidding wars often make buying new attractive. Your best bet these days is to beat the machine strippers at their own game and buy the used equipment at the same auctions they do. This isn't always easy, as you either need to be retired or working such that you have a lot of freedom to attend these sales.

The other problem is that these machines generally require significant handling effort. Plus you have to tear them apart to get to the good stuff.

.
McMaster Carr ships out of New Jersey. I get parts in one day. Cost a bit more, but I get them fast.

All of the big suppliers to machinist and automation suppliers seem to be very capable these days when it comes to quick.

Definitely. I get stuff from THK and Misumi and Lin Engineering, no problem. I've spoken with engineers at Parker and Kollmorgen, and they've been kind to answer my questions. Kuroda on the other hand, don't want to know me. The amount of vendors on Aliexpress you can deal with directly, for example, is mind-boggling. There are tons of great deals in the automation surplus warehouses, if you know what to look for.

This is key you need to know what to look for or ask for. In many cases the companies can't or won't help you. Often they don't know the answers. Just as often they don't have the time to do engineering for a potential customer.

[wizard]

I hope this doesn't come off wrong but you might want to consider that your personality isn't suitable for DIY CNC builds. It might be easier to just buy a new machine and pay for that assembled machine.

I've always thought of Aliexpress as the spiritual home of the Internet scammer. One of my other hobbies is air guns and a lot of people buy high pressure Chinese compressors off that site but I have never been brave enough.

For most Chines products you can find a USA supplier that takes most of the risk for you.

On the other hand there are many vendors that have an excellent track record. The various online forums can help with finding those vendors. Beyond that you seem to have some very negative thinking going on here.

Apparently if you use a prepaid credit card, the risk is not too bad.

That is one approach. Buying international though has a lot of issues that must be considered and for some stuff it is advisable to get professional help. If you are about to spend $5000 on a mill you want to be able to handle all taxes and duties properly.

My views on ordering from Chinese vendors has been colored a little by the overwhelmingly negative experiences I have had in the past - vendors from there always seem to tell me what I want to hear and then send me something that is well below my expectations.

And this has never happened with US based vendors? Seriously though it sounds like you are either hooking up with the wrong vendor or are not communicating well. Based on this thread i think you need to work on how you ask for things. Contrary to popular belief people can not read minds! You cant really expect people to supply you with what you want if you do t ask them in a way that jives with their back ground. We can help some here and with the right descriptions may be able to point you to a common product that might do the job.

The recent example here is the Unistruct right angle bracket talked about earlier. You could easily walk into a supplier of such material and never have the guy behind the counter make the connection as to what you really wanted. The idea popped into my head because Unistrut is all over the place at work. The point is a supplier could have what might work for you but if you don't ask for it in a way that clicks for them no sale will be made.

My expectations are probably the problem.

Mist certainly! To get anywhere with this project you need to know what to ask for with the various vendors out there. It isn't up to them to figure out your needs.

I think that a good deal is when you get the same quality for less money. If someone sends me a lower quality product for less money, I don't consider it cheap. I just expect silver to cost less than gold. I usually feel ripped off and regretful with anything I have ordered from China.

So what you are saying is that you look for the cheapest vendor possible and then expect gold standard parts. Seriously who has the problem here? Frankly the good stuff from China costs mire just like it does anywhere else in the world.

I have ordered a lot of stuff from McMaster Carr and I agree 100% that they are a top quality outfit. Never had an issue and they always exceeded my expectations on delivery times and service. They aren't exactly cheap though.

Actually they are, at least at times. When you compare the cost of nuts and bolts from a local hardware store McMaster is cheap and you get better quality. No you don't get China direct prices but if all you are looking for is cheap you are off on the wrong foot from my perspective.

I think I got a good deal on my THK rails off eBay. I bought used ones but I know so little about rails that I have no clue if I really did well. They all seem very sturdy and well made. The bearing slide smoothly but I don't know what else to look for.

Why the obsession with "doing well". You are happy with the price and quality - move forward.

[Goemon]

I hope this doesn't come off wrong but you might want to consider that your personality isn't suitable for DIY CNC builds. It might be easier to just buy a new machine and pay for that assembled machine.


For most Chines products you can find a USA supplier that takes most of the risk for you.

On the other hand there are many vendors that have an excellent track record. The various online forums can help with finding those vendors. Beyond that you seem to have some very negative thinking going on here.

That is one approach. Buying international though has a lot of issues that must be considered and for some stuff it is advisable to get professional help. If you are about to spend $5000 on a mill you want to be able to handle all taxes and duties properly.

And this has never happened with US based vendors? Seriously though it sounds like you are either hooking up with the wrong vendor or are not communicating well. Based on this thread i think you need to work on how you ask for things. Contrary to popular belief people can not read minds! You cant really expect people to supply you with what you want if you do t ask them in a way that jives with their back ground. We can help some here and with the right descriptions may be able to point you to a common product that might do the job.

The recent example here is the Unistruct right angle bracket talked about earlier. You could easily walk into a supplier of such material and never have the guy behind the counter make the connection as to what you really wanted. The idea popped into my head because Unistrut is all over the place at work. The point is a supplier could have what might work for you but if you don't ask for it in a way that clicks for them no sale will be made.

Mist certainly! To get anywhere with this project you need to know what to ask for with the various vendors out there. It isn't up to them to figure out your needs.

So what you are saying is that you look for the cheapest vendor possible and then expect gold standard parts. Seriously who has the problem here? Frankly the good stuff from China costs mire just like it does anywhere else in the world.


Actually they are, at least at times. When you compare the cost of nuts and bolts from a local hardware store McMaster is cheap and you get better quality. No you don't get China direct prices but if all you are looking for is cheap you are off on the wrong foot from my perspective.


Why the obsession with "doing well". You are happy with the price and quality - move forward.

You shouldn't talk to people like that. It detracts from the friendly nature of online forums and adds no value. You spend all that time writing a reply and took up all that space without including a single helpful piece of information. What for?

Honestly.... nobody cares about your opinion on whether their personality is right for DIY CNC or not so keep it to yourself.

If you find my style of asking for help to be objectionable then go and do something else. I'll be just fine without your helpful insights....

[louieatienza]

I hope this doesn't come off wrong but you might want to consider that your personality isn't suitable for DIY CNC builds. It might be easier to just buy a new machine and pay for that assembled machine.


For most Chines products you can find a USA supplier that takes most of the risk for you.

On the other hand there are many vendors that have an excellent track record. The various online forums can help with finding those vendors. Beyond that you seem to have some very negative thinking going on here.

That is one approach. Buying international though has a lot of issues that must be considered and for some stuff it is advisable to get professional help. If you are about to spend $5000 on a mill you want to be able to handle all taxes and duties properly.

And this has never happened with US based vendors? Seriously though it sounds like you are either hooking up with the wrong vendor or are not communicating well. Based on this thread i think you need to work on how you ask for things. Contrary to popular belief people can not read minds! You cant really expect people to supply you with what you want if you do t ask them in a way that jives with their back ground. We can help some here and with the right descriptions may be able to point you to a common product that might do the job.

The recent example here is the Unistruct right angle bracket talked about earlier. You could easily walk into a supplier of such material and never have the guy behind the counter make the connection as to what you really wanted. The idea popped into my head because Unistrut is all over the place at work. The point is a supplier could have what might work for you but if you don't ask for it in a way that clicks for them no sale will be made.

Mist certainly! To get anywhere with this project you need to know what to ask for with the various vendors out there. It isn't up to them to figure out your needs.

So what you are saying is that you look for the cheapest vendor possible and then expect gold standard parts. Seriously who has the problem here? Frankly the good stuff from China costs mire just like it does anywhere else in the world.


Actually they are, at least at times. When you compare the cost of nuts and bolts from a local hardware store McMaster is cheap and you get better quality. No you don't get China direct prices but if all you are looking for is cheap you are off on the wrong foot from my perspective.


Why the obsession with "doing well". You are happy with the price and quality - move forward.

With a large overseas purchase, it helps to seek the counsel of a customs broker. One screw up, if you're not attentive can have your items held for months.

You can buy Unistrut angle at the local big-box hardware store.. Or maybe they have Kindorf... same stuff, different maker. I believe someone here built a router using Unistrut a while back; thought it was a pretty good idea for something inexpensive for light duty.

[nummi]

I was curious about how stiff carbon fibre plate would be. Young's modulus of carbon fibre is actually a bit less than steel's 181 vs. 200 Gpa. Fibers could be oriented in some structures producing higher value but probably not when building gantry plate. Strenght is many times better compared to steel, but that is not relevant in this case.

I used spreadsheet made to compare gantry shapes. If I interpret this right it seems that when comparing torsion stiffness of 80x150x5 mm RHS to steel plate, the plate needs to be 150x61 mm. Carbon fiber plate would have to be even a bit thicker. I'm not a mechanical engineer so please correct me.

[Goemon]

I was curious about how stiff carbon fibre plate would be. Young's modulus of carbon fibre is actually a bit less than steel's 181 vs. 200 Gpa. Fibers could be oriented in some structures producing higher value but probably not when building gantry plate. Strenght is many times better compared to steel, but that is not relevant in this case.

I used spreadsheet made to compare gantry shapes. If I interpret this right it seems that when comparing torsion stiffness of 80x150x5 mm RHS to steel plate, the plate needs to be 150x61 mm. Carbon fiber plate would have to be even a bit thicker. I'm not a mechanical engineer so please correct me.

Carbon fiber (and all woven composite reinforcements) are strongest in the direction of the weave. If you laid all your fabric in the same direction then most of it's strength would be in that direction but.... nobody who knows what they are doing would lay all their fabric in one direction if they expected multi-directional strength.

When I make cf plates, I take a number of steps to increase the multi-directional strength. First, I switch the direction of the weave for each layer. Second, I add some layers of biaxial and triaxial carbon fiber. Third, I thicken the plates with layers of recycled no-woven carbon fiber mat which, instead of a one-directional weave pattern, it has the fiber laid out in a random matrix which adds rigidity in every direction (as well as reducing cost as this material is very thick on it's own). Fourth, I add carbon nanotubes to the resin which increases rigidity by approx 30% (depending who you ask and if you are buying or selling).

The choice of weave also also makes a huge difference. When I want the most rigid parts possible, my preferred fabric for the outer cosmetic layers is a 4x4 twill which comes out noticeably more rigid than the more common 2x2 twill and plain weaves.

There is also the type of resin to consider. I don't just mean epoxy or polyester resin. There can be huge differences in the physical properties just between epoxy resins. And... don't get me started on the curing schedules

All this makes accurate strength comparisons extremely difficult. Carbon fiber, as a general point is stronger than steel by both weight and volume. But... for reasons described above, you can't say by how much unless you have the two parts side by side to compare.

You also have the added complexity of people using alloys rather rather than pure metals these days. I read about a recently created aluminum alloy that is stronger than steel and titanium. I've had bars of T6 that felt stronger than some low quality stainless steel products I've seen. Plus, the strength of steel is also somewhat dependent on how it's made and prepared too. There is a world of difference between, for example, the differentialy tempered, folded and laminated steel on my old martial arts practice sword and the cheap nasty Chinese stainless steel on the kitchen knives I got as a wedding gift from my distant relatives...

Anyway, net net, if made properly, my cf parts will be stronger and lighter than equivalent steel ones. That's the part I know. The part I am assuming (based on what I've been told) is that a lighter gantry will increase speed.

Also, carbon fiber is less sensative to heat distortion than steel so it should be a generally more stable material for this purpose. It doesn't rust either, which is a plus because I want to put this machine in my garage.

[louieatienza]

Carbon fiber (and all woven composite reinforcements) are strongest in the direction of the weave. If you laid all your fabric in the same direction then most of it's strength would be in that direction but.... nobody who knows what they are doing would lay all their fabric in one direction if they expected multi-directional strength.

When I make cf plates, I take a number of steps to increase the multi-directional strength. First, I switch the direction of the weave for each layer. Second, I add some layers of biaxial and triaxial carbon fiber. Third, I thicken the plates with layers of recycled no-woven carbon fiber mat which, instead of a one-directional weave pattern, it has the fiber laid out in a random matrix which adds rigidity in every direction (as well as reducing cost as this material is very thick on it's own). Fourth, I add carbon nanotubes to the resin which increases rigidity by approx 30% (depending who you ask and if you are buying or selling).

The choice of weave also also makes a huge difference. When I want the most rigid parts possible, my preferred fabric for the outer cosmetic layers is a 4x4 twill which comes out noticeably more rigid than the more common 2x2 twill and plain weaves.

There is also the type of resin to consider. I don't just mean epoxy or polyester resin. There can be huge differences in the physical properties just between epoxy resins. And... don't get me started on the curing schedules

All this makes accurate strength comparisons extremely difficult. Carbon fiber, as a general point is stronger than steel by both weight and volume. But... for reasons described above, you can't say by how much unless you have the two parts side by side to compare.

You also have the added complexity of people using alloys rather rather than pure metals these days. I read about a recently created aluminum alloy that is stronger than steel and titanium. I've had bars of T6 that felt stronger than some low quality stainless steel products I've seen. Plus, the strength of steel is also somewhat dependent on how it's made and prepared too. There is a world of difference between, for example, the differentialy tempered, folded and laminated steel on my old martial arts practice sword and the cheap nasty Chinese stainless steel on the kitchen knives I got as a wedding gift from my distant relatives...

Anyway, net net, if made properly, my cf parts will be stronger and lighter than equivalent steel ones. That's the part I know. The part I am assuming (based on what I've been told) is that a lighter gantry will increase speed.

Also, carbon fiber is less sensative to heat distortion than steel so it should be a generally more stable material for this purpose. It doesn't rust either, which is a plus because I want to put this machine in my garage.

When you talk about speed, are you referring to cutting speed? Or rapids speed? You may want to do some research into what materials you want to cut, and what tools and what diameter of tools you need to cut those materials. That will determine the speeds you need to cut. You then size your motors based on what your components weigh on each axis and how much force you'll need to move each axis; which will determine the RPM you need from your drive motors, as well as the torque at that RPM. With steppers, the rapids end up being a "bonus", as you want to set the rapids speed a small percentage below the maximum speed that axis will move without stalling.

Let's take a couple scenarios about the machine you envision. On the first, the gantry is the short axis (I believe you wanted a work envelope of 30" x 8" x 1.5".) It would be useless to have high rapids on such a short axis of, let's say 10" overall travel, unless you were doing something like raster engraving with a laser. Moving that gantry along the long axis, there would be no need for high rapids, unless you have the odd requirement of machining a little on one side, then going to the other end and machining a little, the going back, et cetera. You'd program the toolpaths to go from one end to another. The only time you'd get benefit from the rapids would be homing at the end of the job.

Let's take another scenario. The gantry is the long axis. Here it wouldn't make sense to me to make the gantry moving, because it only has to move about 10". You'd have a stiffer assembly making the gantry fixed and moving the table. Here though, since the gantry is fixed, the weight doesn't matter. The Z carriage assembly, however, would be affected by weight moving in the long direction. But since that would be lighter than even a small moving gantry, it shouldn't be hard to get that moving fast.

A fair amount of your speed will be determined by the screws you use. If you use precision ACME with anti-backlash leadnuts, expect about 25-40% efficiency with 2-start, to about 70% efficiency with 8-start. Rolled ballscrews are about 90% and ground can be about 95%. Ballscrews will ensure that the majority of the torque your steppers have is used to get that axis moving, not overcoming the friction of the AB leadnuts. The common solution in the DIY CNC world is to use the coarser pitch screw, to gain speed and utilize the low speed torque of the steppers. You'll have to do some rough calculations based on the torque-speed graph of your steppers, and the amount of force needed to move each axis. But again, you should "engineer" your motion system based on how fast your cutting speed needs are, NOT for maximum rapids.

If I remember correctly, my Z carriage assembly - including the weight of the two 7-1/2" long LM block on the gantry, saddle plate, carriage plate, Z axis LM rails and blocks, router mount, router, stepper, stepper mount, coupling, ACME screw and leadnut, screw bearing block - was around 30lbs. I was able to push that whole thing 750ipm rapids with a 48V PSU, G540, 400in-oz stepper, and a 1/2"-8 start screw (1" lead) and cut ash at about 150-200ipm with a 1/2" bit taking 3/8" passes. Of course, my main goal was to cut wood, and I was happy with .003-.005" accuracy since I was still doing finish sanding. I built a small router with 2-start ACME (.25" lead) and 180in-oz steppers at 48V with Leadshine DM542 drives and was able to rapids over 500ipm in tests, and 400ipm reliably. There, I believe my whole carriage assembly weighed in around 15lbs. Note though that these were high end Kollmorgen CTM series steppers, with some pretty impressive torque curve, and I probably could have ran them faster with ballscrews and 75V drive/PSU. Not the weight of steel, but still had some heft. But here, my main concern was having enough torque to move my axes and that tool through the material and have enough reserve to keep position and not jump. Here in my experience mass can be a friend. I wish I could have all the weight of the machine right at that cutting tool. Higher mass means higher inertia, and while that means the axes need more torque to get them going, it also means they are more resistant to bouncing "off course." Think of a car on a track, hitting a car stuck on the track, at about 10mph. The car on the track would probably bounce off depending on the orientation of the other car. Now think of a freight train, hitting that same car at the same speed. That train would still be traveling straight on the track, and either push that car aside, or drag it down the track for a half mile.

[Goemon]

CNC Router Parts sells them, but you have to see if they match up with the rated current on your steppers. You only need to solder pins 5-9, and bridge the resistor on pins 1 and 5. Soigeneris makes a DB9 breakout board with asjustable resistor that fits in DB9 cover..

You don't necessarily need the resistor unless your motors are rated less than 3.5A, but you'll deactivate idle current reduction...

So it says that my 381oz motors draw exactly 3.5a per current. Does that mean I don't need resistors?

If I need them, how do I know which ones match that motor? I know this is probably a super basic question for people who know electronics but I don't. I have a box of resistors here from an old arduino kit but none of them are labeled 3.5a or anything else related to the numbers advertised for my motors.

I have a bunch of 18g wire here and a box of db9 breakout boards from my arcade building days. Making up the rest of the cable will be easy if I know what resistors to use. If they just connect to some of the pins, I won't even have to use a soldering iron. They will go straight into the screw terminals.

[louieatienza]

So it says that my 381oz motors draw exactly 3.5a per current. Does that mean I don't need resistors?

If I need them, how do I know which ones match that motor? I know this is probably a super basic question for people who know electronics but I don't. I have a box of resistors here from an old arduino kit but none of them are labeled 3.5a or anything else related to the numbers advertised for my motors.

I have a bunch of 18g wire here and a box of db9 breakout boards from my arcade building days. Making up the rest of the cable will be easy if I know what resistors to use. If they just connect to some of the pins, I won't even have to use a soldering iron. They will go straight into the screw terminals.

The size resistor you need is in the G540 manual, pretty easy to figure out. You can run the steppers without the resistors, but that will disable the idle current reduction function on the G540... therefore the steppers will run hotter. But since the steppers you have are likely wired bipolar series I don't think it's too bad a problem.