1 Week Ago #1
I have a home made 3 axis wood router (working area 1100mm x 700mm).
It is now basically an extremely competent machine having been upgraded over the months & years.
What I do suffer with is lash (to be expected at speed) on my long (x) axis, this uses Trapezoidal ACME threaded bar (yes I know but it was cheap and has worked up to now).
I'd like to change the x and maybe the y axis to rack and pinion.
I've looked at the commercially available stuff and am not sure that I can easily make the available profiles work with my machine and it is pretty expensive.
Has anyone made their own rack in Acetal? I have machined a fair bit of Acetal on this machine and always had good results.
Any comments or tips?
Last edited by davo453; 1 Week Ago at 04:59 PM.
1 Week Ago #2
If everything else is working fine, then a quick improvement would be to make an anti-backlash nut assembly out of acetal. Make a couple of nuts with some kind of mechanism to close them together - on my first machine I used a couple of bolts with appropriate locknuts to pull the nuts together via clearance and tapped holes in the nuts. Not a perfect solution but something you could put together very easily. At a pinch, you can make a tap for acetal from an offcut of the leadscrew material - no need for hardening for that job. Probably a whole lot easier than trying to get backlash out of a rack and pinion setup - there's a reason why R&P tends to be used only on larger machines where leadscrews are too long for practicality. Looks easy but mechanically there are a few things that can bite you in the bum.
1 Week Ago #3
Thank you for the reply, my present set up has Delrin/Acetal backlash nuts these I made by melting the plastic on to some scrap lead screw and machining the resulting mess to fit. It has proven an almost perfect solution in fact and although this machine has run in excess of 1000 hours now they still don't have any perceptible backlash just a little silicone grease occasionally and all has worked well.
It's not backlash that I am trying to eliminate it is rod lash, as you probably know when you spin a rod at speed and when it exceeds a certain length it starts to wip and that causes a bounce effect at the tool. Hence my looking into Rack and pinion and I may increase the size of the machine at some point in the future too.
I'll just experiment a bit I think.
1 Week Ago #4
I had a little play with R&P a couple of months ago whilst looking at all sorts of possibilities for making a small router. Have a look here it's a good place to design your own gears as they output the result as a DXF or DWG (can't remember which now!!)
Below is a small one I cut out of 6mm thick Acetal as a trial, I think with a 2mm end mill.
1 Week Ago #5
That's a good site thank you and your test looks good.
I ran a few this morning and think it will work well, I'm planning on using commercial metal gears on acetal rack, should be relatively low noise as well.
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1 Week Ago #6
I'd make a delrin nut. I used ordinary threaded rods in my first CNC and cut off a piece of the rod and made a tap out that and with the help of that tap I made delrin nuts. The nuts had really zero backlash for about a year, until I replaced all the threaded rods with ball screws. It served me well and the reason to replace was not backlash or accuracy issues, but simply speed and rigidity. The ball screws I am using now are 1605 and the rods were 12mm, which have a thread pitch of 1.75mm. Of course, the ballscrew/ballnut combo is much better, but on low budget threaded rods and custom made nuts are REALLY very good. Easy to replace the nuts, you can make a new one after a while, and it is really easy to make a tap if you have a piece to spare. There are many other methods of making a zero backlash nut out of delrin, and delrin is excellent for the purpose since it has low friction.
I would not make a rack out of Acetal (Delrin), I don't think it is good for that purpose, but it is suitable for making zero backlash nuts out of it.
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1 Week Ago #9
If screw whip is your problem rather than backlash then making spring loaded screw support might be worth looking at.? But other than this I wouldn't mess around with R&P.
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