Purchasing the right linear rails for a home made cnc router table

[MajorTendonitis]

Guys , I was debating to build a Joe's CNC , and while Joes V bearing Evolution is all that I would probably ever require, the more I study , I'm certain I could build a cnc table myself using square block linear rails , and CNCRP pro series rack and pinion .
Sorry if my terminology isn't great yet .

My design was to have a cutting area of 4' x 5' , as a 4/8 will not fit well in my garage . I'm interested in 3D carvings and signs , and fairly good repeatability. Will be using Nema34 for steppers , aluminum extrusion most likely from Vancouver , as I'm located in eastern BC Canada .

Was hoping to get get opinions on these linear guides and blocks in this link below .

https://motionconstrained.com/store/...linear-guides/

I'm not sure if this is there lower model ? I have heard where 25mm are overkill and 20mm are fine , but I would prefer to go with these , as the cost difference isn't a lot.
Also heard mention that you should exceed your cutting area by approx a foot on each axis for the linear guide length in order to compensate for the area lost to the blocks .

Thanks in advance all , as I've gotta start somewhere

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[ger21]

If you look at the technical info on that page, it explains what the different letters mean.
At the end of the number, ZA means medium preload, which is good.
C means standard precision, which relates to the height of the block. How much they can vary between blocks.

Ideally, you want double seals, or double seals + scrapers. My guess is that these don't have double seals. But you may be able to buy double seal kits and add them yourself, but that can add $20 or more per block.

While the price difference between 20mm and 25mm is small, you really don't gain anything, so your just wasting money. A single 20mm block can carry 4000 lbs. A 25mm block can carry almost 6000 lbs.

[MajorTendonitis]

Thanks Gerry , I had no idea about the seals either

[louieatienza]

Well, if your cutting area is 4' x 5', you have to consider the largest tool diameter you're going to use, plus over-travel for limit and home switches (though with Mach3 and others you can use limit switches as home switches.) You may have to "lead in" to the edge of a workpiece and that adds additional travel. Add to this, the width of the extremities of your bearing blocks. If the spindle center is outside the footprint of the bearing blocks, that too will require more travel. The seals will add to the block footprint. Every inch wasted is money...

[MajorTendonitis]

Well, if your cutting area is 4' x 5', you have to consider the largest tool diameter you're going to use, plus over-travel for limit and home switches (though with Mach3 and others you can use limit switches as home switches.) You may have to "lead in" to the edge of a workpiece and that adds additional travel. Add to this, the width of the extremities of your bearing blocks. If the spindle center is outside the footprint of the bearing blocks, that too will require more travel. The seals will add to the block footprint. Every inch wasted is money...

Wow , some great points

[ger21]

+1 What Louie said. I meant to add that about the length.
You really need to have a complete design to know exactly what you need.

Or, you need to design around a certain length rail, and the travel you end up with is what it is.

I like to have be able to reach at least 2" all around the spoilboard.

The seals will add to the block footprint.

About 1/8", maybe.

[MajorTendonitis]

I see where you definetly need a design . As you guys mentioned, I have to figure out is total distance on the outside of the blocks on each axis , plus where does the spindle sit in relationship to it all .
I noticed the rail wasn't a huge price increase adding a little extra length , but extrusion will be .

My main concern was getting the spindles centre of gravity right , meaning ideally having it in the middle of the bearing blocks on the Y axis.
I wanted to take the easy way out and mount the horizon beam for the X axis to the front of the vertical extrusion thats mounted to the Y axis plates . This will put the spindle forward though .

I see cncrp pro pro version has fabricated a plate of some sorts to secure the main gantries beam directly on top of the vertical extrusion. I guess I could use guzzets

[MajorTendonitis]

(though with Mach3 and others you can use limit switches as home switches.) ..

Not that it changes anything design wise , but as per ger21 , I was going to use UCCNC

[ger21]

my main concern was getting the spindles centre of gravity right , meaning ideally having it in the middle of the bearing blocks on the Y axis.

It's really not that critical, especially when using linear rails. Generally, the gantry beam sits over one of the blocks, which puts the spindle somewhere between the two blocks.

If you look at a side view of my gantry, the spindles will sit slightly in front of the blocks.
http://www.cnczone.com/forums/cnc-wo...ml#post1181528

[MajorTendonitis]

Hi! It is good to build your cnc router by yourself. If you are finding linear lead rails for wood cnc router of which size is smaller than 4ft*8ft, it would be better to adopt 20mm leadrail and blocks because it is enough and would save your money. To be frank, i am a staff from FALA CNC, which is a Chinese CNC router manufacturer.

I'm not a rich man , but I'm just not seeing a big price difference when jumping from 20mm to 25mm ? To me , over designing is better than under designing ?

[ger21]

It's your money.

My point is that if the machine frame was strong enough, you could literally hang a car off of the 20mm rails, and be well under their load limit. your machine will be operating at about 5% of the rated load limits of 20mm rails. If you want to spend a little more, feel free. But there will be zero noticeable difference.

There wouldn't be any difference between 15mm and 25mm rails, on a DIY machine.

[MajorTendonitis]

It's your money.

My point is that if the machine frame was strong enough, you could literally hang a car off of the 20mm rails, and be well under their load limit. your machine will be operating at about 5% of the rated load limits of 20mm rails. If you want to spend a little more, feel free. But there will be zero noticeable difference.

There wouldn't be any difference between 15mm and 25mm rails, on a DIY machine.

I read a post one time of someone having issues with the hardware for the holes in the rails , as there were certain sizes , and one worked better than the other with extrusion. But I think the holes are the same diameter , so I'd have to check that out . If everyone is against using 25mm guide rail , I'll certainly consider going with 20mm .

Guys , is there a recommended carriage you can buy for the Z axis that fits a 100mm spindle that is ready to be bolted up to the X axis plate? I don't really want to build that and would prefer to buy a complete one .

[jfong]

I used some 15mm THK and more than adequate load handling ability on my extrusion router. However my next gantry router is using 20mm and 25mm rails because the 5&6 mm tapped holes are easier to do than the 4mm ones used on the 15mm rails. I broke a couple of taps before.....

I found the NSK 25mm (1200mm long) rails on eBay for cheap. Would rather of used 20mm since the carriages are much shorter. I would lose less travel.

[ger21]

Velox sells a complete Z axis that the Joe's guys use.

Yeah, the 15mm ones are tricky because of the small screws, but 20mm and up are fine.

I'm not against using 25mm, they're just unnecessary.

[MajorTendonitis]

Yes to my suprize I recently heard cncrouterparts uses 20mm rails . Good to know about the screws , as I wasn't sure which ones were causing some people grief .
Never thought about the blocks being shorter for the 20mm rail also , will have to check that, although I don't think it will be to much of an issue.

Regarding Z axis , thanks for the heads up . Will check them out

[MajorTendonitis]

I'm assuming a guy wants the four bearing setup , as in theory it would have be more stable flex wise .Not understanding which screw pitch is preferred though ?
I'm shooting for 8" of travel

[jfong]

I think one one reason why cncrouterparts choose to use 20mm rails is that they are just wide enough to sit flat in the narrow extrusion slot that they use.

I had to make a larger flat aluminum mounting plate for my 15mm rails so they can be attached to the extrusion. Using 20mm rails would of avoided all that extra work.

[MajorTendonitis]

I think one one reason why cncrouterparts choose to use 20mm rails is that they are just wide enough to sit flat in the narrow extrusion slot that they use.

I had to make a larger flat aluminum mounting plate for my 15mm rails so they can be attached to the extrusion. Using 20mm rails would of avoided all that extra work.

That's good to know , and something that would have been totally unexpected till I got to that point. Thanks again for all your info guys

[jfong]

Here's a good video of a cncrouterparts machine being put together. Lots of interesting design choices.

[MajorTendonitis]

Here's a good video of a cncrouterparts machine being put together. Lots of interesting design choices.

Have had him in my favourites for a while now
I watched him build a Joes Evo cnc first , then apparently he sold it and assemble the pro version from cncrouterparts. Pretty smart guy imo .

I guess he didn't like the V bearing system on his Evolution machine ?

I know he had issues with welding up the frame on the Evo , some warping which seems to be problematic for most considering the heat involved as your welding .
Nothing he couldn't fix with spacers , but I'd sooner build the framework under the spoil board from extruded aluminum.
I want to build the base underneath the frame from wood though .