Limitations of cheap 4th axis components off eBay?

[awerby]

Thanks. That looks like a great option for me if the quality is right. It's both affordable and modular. I like the idea of being able to upgrade the mounting plate and the motor to fit my needs. I also like the idea of a made in America product from a company that would stand behind their product.

Do you own this unit yourself?

[Actually, I have several of them. Taig uses the manual version as a basis for their 4th axis, putting on their own base-plates and motor mounts.]

How would you mount a 2" x 6" x 12" slab of aluminum (or wood) as the work piece with a unit like this? Would you attach tubes on either side (of the blank stock) to fit the chuck and tail stock? Or would you mount something else (instead of a chuck) to the mounting plate? I have seen work holders on wood lathes that look like round plates with nail spikes sticking out to grip larger slabs of wood for turning.

[Those are called headstock spurs. They work well for soft woods, but not on aluminum. The easiest way to do this is to screw a square-section piece of stock to the headstock end of the workpiece and hold that in a 4-jaw chuck. If screws can't be used, you can also cut down the workpiece to a square stub that fits the chuck. I've also done more elaborate fixtures, like a tapered dovetail mount that accepts a dovetail screwed to the workpiece, but that took some machinery to build.]

I am trying to figure out if a 4" or 5" chuck is sufficient for what I intend to work on or if the chuck diameter has to (at least) match the diameter of the blank stock.

No, there's no fixed rule like that.

[bill south]

Goemon;
Remember all the available talent and willingness to help we enjoy here on the zone. Why not gather your components, draw up whatever coupling you think will work and post here under the Request for Quote (RFQ) thread/ You may be surprised at the inexpensive help that is available from one zone member to another. Heck, once a functional system is complete, draw up complete plans including part numbers and sell it on flea bay. I would pay $$ for a set of viable plans!
Just a thought.
Good Luck.
Bill

[ger21]

Where did the blue headstock base come from? Is it something you build or repurposed from something else?

This was is based on a harmonic drive transmission that came off ebay for $100.

It's a gearbox, made by Harmonic Drive.

[wizard]

I hope that I can offer something to this thread to help. Just remember there are many many ays to accomplish something like this, one answer isn't the end of the story. You need to find the best fit for your intended usage.

Thanks. That looks like a great option for me if the quality is right. It's both affordable and modular. I like the idea of being able to upgrade the mounting plate and the motor to fit my needs. I also like the idea of a made in America product from a company that would stand behind their product.

Yeah finding companies that actually stand by their products isn't easy anymore.

Do you own this unit yourself?

How would you mount a 2" x 6" x 12" slab of aluminum (or wood) as the work piece with a unit like this?

This is just like learning to be a machinist using a lathe, there is generally more than one way to get something done. If your chick isn't being enough you can consider using a faceplate for example. Keeping with our lathe based mind frame consider finding a lathe operators manual, Southbend use to publish one that was called " How to Run a Lathe" if I remember correctly, or look for the many web sites out there. In any event work holding is a broad subject that takes some time to master.

Would you attach tubes on either side (of the blank stock) to fit the chuck and tail stock? Or would you mount something else (instead of a chuck) to the mounting plate? I have seen work holders on wood lathes that look like round plates with nail spikes sticking out to grip larger slabs of wood for turning.

There are many many approaches here. For wood turning you often screw the workplaces to a face plate and in fact you can do similar with metal parts by drilling and tapping. There are a number of variants even when it comes to face plate usage, for example sometimes people will glue the work piece to the intermediate piece bolted the chuck, usually with a paper layer to permit splitting off later.

Barbed dogs are for use when spinning between centers.

I am trying to figure out if a 4" or 5" chuck is sufficient for what I intend to work on or if the chuck diameter has to (at least) match the diameter of the blank stock.

Ideally you want to avoid excessive hangout of the chucks vise jaws. This is for personal safety but also prevents damage to the jaws or the chuck from excessive stresses. Generally you want to go to a bigger chuck if the jaws hang out too much. How much is too much? That depends upon the chuck and its design, I get bothered if the jaws hang out more than the width of the top step and even that can be too much on some chucks.

Now that's what I am talking about! I was wondering why we don't see more diy projects for 4th axis builds.

There are lots of examples if you start searching the net. Also Similar units are often built by welders as fixtures for rotation of work pieces as they are being welded. Don't laugh at the idea of a weldor building such things because I've seen some pretty impressive homemade solutions.

The obvious question is what tools you needed to make the coupling components. My manual metal working skills are very limited and there is little to no obvious availability of off the shelf coupling components to go directly from stepper to decent sized lathe chuck.

You wouldn't want to go directly to a stepper in most cases anyways. The resolution isn't that good (200 steps per rev) and generally. you want to maximize torque to resist rotation of the work piece due to cutting forces. By the way YES I know about micro stepping but even that doesn't offer a lot of improvement compared to what you actually might need at the work piece. Remember we are talking rotary movement measured in degrees or some part of a circle, 1.8 degrees can be huge on a piece 10 inches in diameter. Ideally you want to see increments in either hundredths or thousands of a degree.

I have a drill press and an angle grinder. I wonder if I could make a less professional-looking version of your coupler... or maybe the timing belt option is a better option for me....

Do consider local machine shops. Given a decent drawing a simple flanged base hub should be rather cheap, but also consider machine component supply houses for what ever they might have available. Even better would be to put a hub on the gear box that takes common lathe screw threads. You can then use faceplates, chucks and other devices that already use that thread standard. The only problem here is that there are a number of common thread sizes in use. You could also consider the simple bolt on flange used on Mini lathes.

A word of warning though, bolted on chucks or faceplates can be a problem on any machine that might want to reverse direction of the spindle. Frankly they can unscrew which will really piss you off, there are ways to address this to some extent but none of them are ideal in my opinion. This is where the Mini lathes bolted on flange is a very good solution for low end indexers. Off course there are other solutions from the world of larger lathes but pieces tend to skyrocket.

Where did the blue headstock base come from? Is it something you build or repurposed from something else?

Not mine. Given that I'd strongly suggest spending time looking at some examples one the net. Try searching for "Rotary Indexer DIY" or "Rotary Table DIY", just adding DIY to the search term will produce dramatically different results and help you avoid the commercial units. I've seen solutions that have used nothing more extravagant than a used gear box and a sheet metal frame for motor mounting to something that looks like a work of art built by a machinists.

[johncarpenter]

Goemon, sorry to be getting back to you late. The blue headstock unit is a "harmonic drive transmission" I got off ebay. It originally had an input shaft and an output shaft. The input shaft was replaced with the shaft of the stepper motor. Actually a lot of work. My next 4th axis will mount a belt sprocket on the input shaft and then mount a stepper motor with sprocket parallel to the harmonic transmission coupled with a belt. Much less trouble I think. If you want to see how much work the in line stepper motor was, the build is detailed on my website at: 4th Axis with Harmonic Drive – Build Log | Carpenterswoodworking.com.

[awerby]

Nice write-up, John! That's definitely a keeper. The advantage of a rotary table built off a harmonic drive is that it eliminates backlash, which would be a problem if you used something like the Sherline rotary table with a toolpath that kept changing directions (fortunately, most don't). You can buy units like that off the shelf, (from places like this one: 4inch Harmonic 4th Axis Set-SKYFIRE CNC ) but I'm sure you saved a ton of money doing it your way.

[Goemon]

Goemon, sorry to be getting back to you late. The blue headstock unit is a "harmonic drive transmission" I got off ebay. It originally had an input shaft and an output shaft. The input shaft was replaced with the shaft of the stepper motor. Actually a lot of work. My next 4th axis will mount a belt sprocket on the input shaft and then mount a stepper motor with sprocket parallel to the harmonic transmission coupled with a belt. Much less trouble I think. If you want to see how much work the in line stepper motor was, the build is detailed on my website at: 4th Axis with Harmonic Drive – Build Log | Carpenterswoodworking.com.

Thanks. I was going to ask if you wrote up the details of the project anywhere. I'm sure I'll be borrowing some of those ideas.

I did a little more research this afternoon and I think I found what I would need to hold the work. These round clamps are made to attach to rotary tables and they are specifically for holding flat stock like, for example, the 2" x 6" x 30" rectangular slabs I would start with:

Caste Iron 100 mm Round Vice for 4" (100 mm) Rotary Table + Fixing T-Nuts

I am thinking about using two identical rotary tables mounted horizontally opposite each other with one of these round clamps on each. Then I could make a buy a coupling piece like your one to attach a stepper motor to one (or both) of the rotary tables.

[handlewanker]

Hi....what is your budget?........in the end you might be spending more trying to make one than actually buying one off the shelf.

If you don't have the skill to work a lathe or mill or have access to them the end result is more than questionable......there is no quick fix to overcome lack of machining skill, only money or kindness can fix that with someone else's expertise.

At this moment in time your starting point would be the EBAY 4th axis offerings at the best price range you can get........a lot will depend on your expectations for the model you choose.

If you find the belt drive stepper type is not all that strong replace the stepper motor with a more powerful one.......that is not rocket science....the basic body, spindle, bearings and chuck are already there.

In the end your investment could be in the region of $500 after motor replacement etc.

OR......you could buy a pair of 25mm bore pillow blocks and build one on an aluminium base plate etc etc.......total outlay with metal bits and pieces, pillow blocks, pulleys, belt, stepper motor and a 100mm chuck, about $350......the chuck itself is $125 near enough.
Ian.

[johncarpenter]

No matter how you clamp you are still going to need to drive the assembly. If you use 100 lbs of force at the bit to stall the motor as your design goal that would be 33.3 ft-lbs of torque assuming a 4 inch radius of work. A typical 425 in-oz stepper (2.2 ft-lbs) will need a 15 to 1 drive reduction to get that torque. 15 to one is a lot for a belt system. You might need a double belt reduction system to get that ratio. And the high gear ratio sprockets are expensive. That is why I used a harmonic drive. Much less complicated. Some of the Chinese 4th axis on ebay have harmonic drives and offer 50 and 100 to 1 reduction ratios. Cost is around $450 delivered. Do the math on your drive system to determine what your drive needs to be for speed of rotation and torque.

[Goemon]

Hi....what is your budget?........in the end you might be spending more trying to make one than actually buying one off the shelf.

If you don't have the skill to work a lathe or mill or have access to them the end result is more than questionable......there is no quick fix to overcome lack of machining skill, only money or kindness can fix that with someone else's expertise.

At this moment in time your starting point would be the EBAY 4th axis offerings at the best price range you can get........a lot will depend on your expectations for the model you choose.

If you find the belt drive stepper type is not all that strong replace the stepper motor with a more powerful one.......that is not rocket science....the basic body, spindle, bearings and chuck are already there.

In the end your investment could be in the region of $500 after motor replacement etc.

OR......you could buy a pair of 25mm bore pillow blocks and build one on an aluminium base plate etc etc.......total outlay with metal bits and pieces, pillow blocks, pulleys, belt, stepper motor and a 100mm chuck, about $350......the chuck itself is $125 near enough.
Ian.

$500 is within my budget range. I was looking at an off the shelf one for $700. I am just trying to understand if I would be able to do what I need with the various options.

Any diy 4th axis I made would largely be dependent on using ready made parts. I never intended to machine custom parts when there are parts that can be bought off the shelf at relatively low cost.

Ready made rotary tables, mounting plates, round clamps, chucks, motor mounts and lathe spindles can all be bought off the shelf. In most cases there seems to be affordable options available.

Obviously just buying a complete 4th axis kit would be easiest but the thing that made me pause and ask for advice is that most ready made low cost CNC kits seem to use low quality parts. It's not an area rich in good deals. Thanks to some good advice from people here and other forums, I have been able to buy better components for the same or less cash by putting my own kits together for other areas of my CNC project.

My understanding, based on what people here have said, is that the potential limitations of cheap Chinese 4th axis kits is a sacrifice of stability, holding torque and precision. I.e. They are fine if you are making a short wooden or plastic action figure but potentially problematic for larger parts made with harder or heavier materials.

I don't expect or need high levels of precision in a 4th axis. I just need it to hold and index 2" x 6" x 30" slabs of hard wood or aluminum with enough stability to machine them into parts with a reasonable finish quality.

Anyway, I think I have a good idea of what would work for me now and as someone said in one of the responses below, there is more than one way to skin this cat.

[Goemon]

No matter how you clamp you are still going to need to drive the assembly. If you use 100 lbs of force at the bit to stall the motor as your design goal that would be 33.3 ft-lbs of torque assuming a 4 inch radius of work. A typical 425 in-oz stepper (2.2 ft-lbs) will need a 15 to 1 drive reduction to get that torque. 15 to one is a lot for a belt system. You might need a double belt reduction system to get that ratio. And the high gear ratio sprockets are expensive. That is why I used a harmonic drive. Much less complicated. Some of the Chinese 4th axis on ebay have harmonic drives and offer 50 and 100 to 1 reduction ratios. Cost is around $450 delivered. Do the math on your drive system to determine what your drive needs to be for speed of rotation and torque.

Most of the rotary tables I have been looking at either come with Nema 23 or 34 motor mounts, or the manual rotary dials can be replaced with motor couplers relatively easily. I need to do more research on motors for this but I will definitely read up on harmonic drive options. My intention is to buy a motor with a lot more torque than I think I might need. The message I have taken away from here is that the more holding torque the better.

Every part I work on is likely to start as a 2" x 6" rectangular slab that is between 12" and 30" in length. That should make it fairly easy to guesstimate the max weight it will need to hold.

[ger21]

I don't expect or need high levels of precision in a 4th axis. I just need it to hold and index 2" x 6" x 30" slabs of hard wood or aluminum with enough stability to machine them into parts with a reasonable finish quality.

As you start to machine these parts, and they start getting thinner, and smaller, the part itself may not have enough rigidity to get a good finish.

[handlewanker]

Hi, just had a brain storm moment.......you could take a small 1/3 HP 3 phase 3,000 rpm motor and mount a chuck on the short end that has the fan.(removed).

The end with the spindle can take the timing pulley and a bracket attached to the flange mount for the stepper.

It would get driven by a stepper motor for 4th axis work as you're just using it as a headstock.

You would want the model with a flange so that the stepper can be fixed to a bracket attached to it etc.

You'll also need a pair of foot mounts too.

If you wanted to do some turning all you have to do is remove the timing belt and add a VFD to control the speed......cost about $100 from Conon in Glen Waverley.....and on EBAY.
Ian.

[dharmic]

Nice and simple. Mind you, if you wanted the lathe spinning at 1800 rpm through a 50:1 harmonic drive on the output of the motor, that motor is going to have to spin pretty fast!

[Lucons]

Hi if you add a 4th axis on long axis, your machine could be a cylinder engraving machine

[wizard]

$500 is within my budget range. I was looking at an off the shelf one for $700. I am just trying to understand if I would be able to do what I need with the various options.

This is the part that is very hard to answer. If I understand you right, machining aluminum is a big part of this devices use. If so you really needs something that will be more rigid than might be suitable for wood working. Especially if I understand your usage here which would be machining gun stock parts out of aluminum solid blanks. IF you want such work done in a timely manner you really need to have half decent metal removal rates and that means feeds and loads higher than would be seen in wood working. On the other hand if you are machining near net shape extrusions you might get buy with a far simpler drive.

Any diy 4th axis I made would largely be dependent on using ready made parts. I never intended to machine custom parts when there are parts that can be bought off the shelf at relatively low cost.

Some machining will be required but if you are really determined a German milling machine will work.

(incase you are wondering a German milling machine refers to an apprentice with a file)

Ready made rotary tables, mounting plates, round clamps, chucks, motor mounts and lathe spindles can all be bought off the shelf. In most cases there seems to be affordable options available.

It is unlikely that all that stuff will fit together without machining. Say for example you purchased a lathe head stock with spindle, How would you attach a pulley or a worm gear to the spindle. This isn't as simple as art looks because the drive pulleys on a lathe spindle often are part of a sandwich fo components that are pulled together with a nut on the end of the spindle to set the preload on the bearings. Making a suitable spacer in this case is a bit more than a German milling machine can handle.����

Obviously just buying a complete 4th axis kit would be easiest but the thing that made me pause and ask for advice is that most ready made low cost CNC kits seem to use low quality parts. It's not an area rich in good deals. Thanks to some good advice from people here and other forums, I have been able to buy better components for the same or less cash by putting my own kits together for other areas of my CNC project.

It is question of volume demand, decent 4th axis cost a lot because the demand isn't there. In a way it is like the issue of the cost of a CNC router, there simply isn't enough volume for people to make a business case with low cost machines. It isn't like buying a drill press where everybody and their brother buys one thus high volumes. So yeah the potential is there to make a better unit, at a lower cost, but doing so implies that you have access to the machinery to do so.

My understanding, based on what people here have said, is that the potential limitations of cheap Chinese 4th axis kits is a sacrifice of stability, holding torque and precision. I.e. They are fine if you are making a short wooden or plastic action figure but potentially problematic for larger parts made with harder or heavier materials.

I don't want to dismiss every unit out of hand but the problem here is that the Chinese are under the same economic realities anybody wanting to produce a low cost fourth axis is. That is how do you make money on such low volume hardware. You either make an incredibly cheap device that barely passes muster or you build something decent and charge a proper price. I'm fairly certain you could find far more robust 4th axis from Chinese machine tool manufactures but you will likely be paying a fairly stiff price for such hardware.

I don't expect or need high levels of precision in a 4th axis. I just need it to hold and index 2" x 6" x 30" slabs of hard wood or aluminum with enough stability to machine them into parts with a reasonable finish quality.

That requires precision and good repeatability. Remember you will likely be positioning in some fraction of a degree, the farther you are away form the center line the bigger that step is. Likewise if you are carving out material using many passes through layers of material you need good repeatability.

Anyway, I think I have a good idea of what would work for me now and as someone said in one of the responses below, there is more than one way to skin this cat.

Yep many ways to a suitable system!!!!

In any event I do have concerns about how stable some of the pieces you will be working on, will be without being supported by some sort of trunnion. I'm fairly sure basic wooden gun stocks will fine but I'm not getting the warm and fuzzies with respect to the metal parts you want to machine.

[handlewanker]

Nice and simple. Mind you, if you wanted the lathe spinning at 1800 rpm through a 50:1 harmonic drive on the output of the motor, that motor is going to have to spin pretty fast!

Hi....no harmonic drive needed or practical if you just have the motor with a timing pulley drive, the harmonic drive is a stand alone device directly coupled to a stepper motor.

The motor I mentioned is purely as a passive headstock but the bonus is that it can also be a lathe in it's own right. with the belt disconnected and 3,000 rpm available.

Someone did say some time back that he was thinking that a double ended bench grinder..... sans stones etc..... could be used too as it's single phase 3,000 rpm and with two spindles is quite adaptable although not practical to speed control.

The bonus also is that both spindles are threaded so fixing a pulley or chuck adaptor is easy peasy.

A 3 phase motor I have is only 100mm diam and 100mm long in the body......it's so almost there that I might give it a go sometime.......timing pulleys are available off the shelf on EBAY.......not my cup of tea, but good for another project to see the wheels going around.
Ian.

[dharmic]

Iain, the problem I see is that a NEMA 23 might struggle to hang onto offset parts during a cut on a 6:1 or similar belt arrangement (at least that's what seems to be happening on my 4A now) so the higher reduction rate is possibly warranted there. A smaller motor on a direct drive spindle on a lathe op might be a bit light on torque so the 2:1 - 6:1 might be pretty nice there. Then you need a way of switching between.

Still. I just bought a $40 ozito (for those playing outside of Oz, Ozito is the equivalent of the cheapest nasty Horror Freight or B&Q have on offer) bench grinder for a tool grinder project and now you've got me looking at it in a different light

[handlewanker]

LOL....Ozito rules.....I have quite a few of their products......not professional stuff, but one, the cross cut drag saw, is a gold mine of opportunity when it comes to accurate wood cross grain cutting.

Yeah, the limitations of the mind is all it takes to get into designing with off the shelf items for quick builds.

I'm doing a 4th axis design build project but keep doodling up new ideas to simplify it and that puts the whole project on the back burner.

The latest doodle is a differential gearbox type, backlash free, with a ratio of 1:18, specifically to interface with a 200 step motor for position control......the 1:18 would also be quite enough reduction for most work.

Then there was the design with the compound gear train, but the gears are hard to come by without actually buying in a gear cutter set and making them myself.

The main aim in all the designs is to have zero backlash and a 1:18 reduction ratio as a prime objective.....so far it's worked out OK on paper.
Ian.

[dharmic]

There was a guy on the SeeMeCNC forum who started off making a 4th axis (I believe?) but then detoured to making boxed carriage ways gibbed with POM (Delrin). I think. He was so happy with the results and kept chasing the rabbit down the hole. He ended up with a metal cutting savage of a 7 axis (I think) mill turn thing which he was using to make hot ends for 3D printers. Only saw one video of it in action but damn, for a home/shop made machine it was impressive.