Joe's. Leadscrew or R&P?

[David Warkentin]

Which version of the hybrid would you recommend and why?

[John McClanahan]

I have a 36x42" router table with ball screws. I found the ball screws on ebay for a price I'm happy with. That said, if I were to build a bigger one I would use R&P. Long lead screws are expensive. Most of the bigger commercially build machines use R&P. I'm sure there is a reason for it.

John

[Mike Heidrick]

You get a lot of whip with long lead screws. You also loose travle to the end bearing blocks on the X and Y axis that you gain with the R&P build. R&P is a faster method of motion vs the spec'd lead screw joes designs. R&P is also cheaper to build overall and there is a LOT less HDPE in the R&P build. For all those reasons build the R&P version.

[Angie Orfanedes]

My understanding is R&P is a necessity for the longer travel machines because of its speed and the whip problems on long lead screws. However, I read somewhere that lead screws have considerably more accuracy over rack and pinion machines. Maybe someone else who has experience with both will chime in.

[Michael Simpson Virgina]

Was just going to post some leadscrew observations when I saw this thread. I am on my 4th build. ( I think. I have lost count). I gave up on a 4'x'4 cutting area with leadscrews. Its just too dang hard to get a good lead screw that does not whiip. It will all depend on how straight the lead screw is. I have 6, 72" 1/2" 8 start lead screws from mcMaster Car and all are not straight. 2 can handle a 54" run at fairly high speed all the others whip so bad the stepper stalls.

If you could possibly get an very straight leadscrew I am sure you could probably get a 72" run which would yeald a 4'-4.5' cutting length but I think you would have to purchase 20 sets to get one that was not bent. All that said. This will not effect cutting speeds just the rapids used for moving from cut path to cutpath. For that reason you need to use at least an 8start screw for a 32" or larger run. This allows the carrage to move faster with the screw moving slower. You wont have as much torque.

So in answer to your original question it depends on the size of your router. IF you are going with the full size 4' x 4' You are goin to have to keep the speed slow or it just will not work.

All that said if you plan on doing a lot of aluminum cutting you should stick with single start lead screws and a smaller bed.

You will probably get less whipping with a ball screw as they are machined and probably be straigher problem is they are hard to get at langer lengths. Trey to find a set of 72" ball screws on ebay. Not going to happen. If you happen to find one it will be very very expensive.

[Michael Simpson Virgina]

Update
With some leadscrew tweeking. I have been able to get 42" cuting travel at 486IPM. On my smaller cnc with same screws/motors I can get over 600 IPM. Since I am only familure with McMaster Carr leadscrews I cant say what you would get with another manufacture.

FYI my carriages are 12" wide with a lead nut on both ends so results will be quite differernt with the Joes Build.

[Scott Shepherd]

Just for the record, ball screws are superior in all aspects, except price. You will not find commercial CNC milling machines (which the CNC router is spawned from) that use rack and pinion for anything. I've run many large machines and all of them had ball screws. I worked for the company that invented a lot of that technology and I've never once seen a rack and pinion system on anything that required speed and accuracy.

Having said that, the mechanics involved to make it all work tend to price it out of the CNC router market. So it's not that ball screws are bad or worse than rack and pinion, it's that for the money, you can't setup the ball screw system properly. So rack and pinion might be better, but it's better because it fits the price point, not because it's a better system.

[Mike Heidrick]

I will just comment that the accuracy of R&P and speed will far outmatch anything I am DIY'ing with a 3hp or less wood router. Without trying, I get 1000 IPM rapids and have just under 2000 steps per inch with my medium range $300 G540 controller and $50 nema23 380oz steppers with $90 3 to 1 nema23 R&P belt reduction and a $100 48V 12amp power supply. I do not posses tooling for a router (my 1/2" max collet) that will let me do the work I do and max out anywhere near the possible speeds and depths of cut in hardwoods and MDF. I surfaced my spoil board to .003" a couple days ago with a $14 chinese 1.75" router bit and could have went to .0003". Not sure of your wood routered CNC work but that is plenty accurate for mine for sure. There are much superior systems for sure. The question is what do I need in my 5'X4' cutting area.

[Scott Shepherd]

I'm not sure how you would measure .0003" in a wood working environment, since anything that can accept moisture can move with a temperature or humidity change, even to a small degree, but if you read what I said, I said R&P might be the best solution for a CNC router, but it's because of price point. Could you build a CNC router with ball screws that would smoke the speed and accuracy of R&P systems? Yes. Would it make sense to do so, no.

[Rob Wright]

Rack and Pinion all the way on the Joe's for the things that were previously mentioned: easier to build and align, faster, less bolts and HDPE. I have a heavily modified machine based on Joe's design. Yes my leadscrew version cut rapid at 500ipm, but my rack and pinion can go 1000ipm on rapids. I can cut full depth in MDF at 300ipm and create nice chips - not dust. The machine does everything that I want it to do. Have fun with the build - it's the best part of it!

[Mike Heidrick]

100% agree with you Scott.

[Dave Spitzer]

You may find this link of interest. http://www.procamcnc.com.au/cnc-mach...k+Vs+Ballscrew

Dave

[Michael Simpson Virgina]

If its going to be a CNC router for wood or plastic I would go with R&P. If you want to cut aluminum then go with single start lead screws and dual lead nuts.