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View Full Version : Workshop made Acetal / DELRIN Rack & Pinion



davo453
17-04-2017, 06:59 PM
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?

Dave

Neale
17-04-2017, 09:32 PM
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.

davo453
18-04-2017, 09:41 AM
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.


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.

njhussey
18-04-2017, 02:09 PM
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 (http://hessmer.org/gears/InvoluteSpurGearBuilder.html) 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.

21417

davo453
18-04-2017, 02:29 PM
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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A_Camera
18-04-2017, 08:49 PM
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.

Boyan Silyavski
18-04-2017, 09:00 PM
I believe that at the current prices 1605 / 1610 screws are the way to go. No way you can convince me that you can not spare 100 pounds for a complete ball screw setup for your machine size. Do a job for sb and with the funds raised make the upgrade. Am i right?

magicniner
18-04-2017, 11:25 PM
It's not backlash that I am trying to eliminate it is rod lash.

Convert to rotating nuts & fixed screws.

JAZZCNC
18-04-2017, 11:26 PM
I believe that at the current prices 1605 / 1610 screws are the way to go. No way you can convince me that you can not spare 100 pounds for a complete ball screw setup for your machine size. Do a job for sb and with the funds raised make the upgrade. Am i right?

Plus 1 on this.! . . . . Not worth messing around with by time bought stuff and messed it up.

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.

A_Camera
19-04-2017, 12:02 PM
I believe that at the current prices 1605 / 1610 screws are the way to go. No way you can convince me that you can not spare 100 pounds for a complete ball screw setup for your machine size. Do a job for sb and with the funds raised make the upgrade. Am i right?

Can you really get such long screws with nuts for 100 including shipping? Otherwise I agree, ball screws are best, but at those lengths I think that screws, nuts and support bearings cost more than 100.

Boyan Silyavski
19-04-2017, 06:49 PM
Can you really get such long screws with nuts for 100 including shipping? Otherwise I agree, ball screws are best, but at those lengths I think that screws, nuts and support bearings cost more than 100.

A bit more than i said, more or less "length in cm"=euro

davo453
19-04-2017, 08:28 PM
All good feedback and food for thought thanks.

From what I can work out ball screw at roughly 1500mm would be around 75 plus the nut at around 60 and I have two on my x axis so it's more like 260 ish.

Guess I am mainly considering r&p because Peter that does the cncnutz YouTube blog has had a good experience with it.




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Boyan Silyavski
19-04-2017, 08:35 PM
Aliexpress (https://es.aliexpress.com/store/product/L900mm-SFU1605-16mm-Ballscrew/210929_1205155651.html?spm=2114.04010208.3.160.4RG X0V&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10 065_10151_10068_10136_10137_10060_10138_10155_1006 2_10156_10154_10056_10055_10054_10059_10099_10103_ 10102_10096_10148_10147_10109_10052_10053_10142_10 107_10050_10143_10051_10084_10083_10119_10080_1008 2_10081_10110_10111_10176_10112_10113_10114_10032_ 10078_10079_10077_10073_10070_10123_10120_10124,se archweb201603_4,afswitch_1_afChannel,ppcSwitch_4&btsid=085d4f14-29e2-449c-ae4f-309d34e26633&algo_expid=7a67473d-94f1-458e-84d3-f6a713561112-19&algo_pvid=7a67473d-94f1-458e-84d3-f6a713561112)has better prices. What speeds your are trying to achieve with that length screw?

JAZZCNC
19-04-2017, 09:47 PM
Guess I am mainly considering r&p because Peter that does the cncnutz YouTube blog has had a good experience with it.

Depends what you want from machine. R&P is much less accurate and far less efficient. Which means the system as whole is worked harder. Motors will be pushed harder which in turn works the drives harder etc etc.
Then you have the complexity of R&P compared to Ballscrews. To get decent resolution you'll 99% have to use ratio which introduces more cost/complexity. Then you have to think about backlash and adjustment vs wear,? Too much adjust and get excess wear. Too little and you get backlash. Then throw into the mix keeping rack clean and free from debris and the verly slight extra cost, if any, of ballscrews is price you should gladly pay.

Like Boyan says go to China and you'll get better price. Go to Bst automation on Ali express and tell Fred Le Dean sent you and might be surprised at the price you get back.!




Just because one person uses it and finds it's ok doesn't mean it's good.

A_Camera
20-04-2017, 06:42 AM
A bit more than i said, more or less "length in cm"=euro

Yes, that's more realistic. Around 300 pounds for the OP. But of course, it is definitely the best solution even if it is more expensive and takes more time and is also more complicated than making three delrin nuts.

davo453
20-04-2017, 11:15 AM
Ok I think you are talking me down and the obvious (Ballscrew) is most probably the way to go.

Thanks for the tip re BST automation.

I've never ordered from Aliexpress anything to watch out for? presumably you are likely to get hit for duty on the import..

A_Camera
20-04-2017, 12:36 PM
All good feedback and food for thought thanks.

From what I can work out ball screw at roughly 1500mm would be around 75 plus the nut at around 60 and I have two on my x axis so it's more like 260 ish.

Will you be upgrading only the X? Also, don't forget to buy machined ball screws AND also support bearings and ball nut bracket, unless you plan on making those. Another thing is that I don't think you should buy 1605 in that length, go for at least 2005.



Guess I am mainly considering r&p because Peter that does the cncnutz YouTube blog has had a good experience with it.
If R&P is good enough or not depends on your requirements. Though, I think I'd personally prefer timing belt and not R&P.

JAZZCNC
20-04-2017, 10:44 PM
Will you be upgrading only the X? Also, don't forget to buy machined ball screws AND also support bearings and ball nut bracket, unless you plan on making those. Another thing is that I don't think you should buy 1605 in that length, go for at least 2005.

If this is a router then wouldn't use 2005, it will be far too slow. Router needs at least 10mm pitch and at this length I'd be inclined to use 20mm pitch with 2:1 ratio to lower screw speed and increase torque.

Should get 2020 screw with end bearings and machined for about 200.

JAZZCNC
20-04-2017, 10:47 PM
I've never ordered from Aliexpress anything to watch out for? presumably you are likely to get hit for duty on the import..

Only thing you'll pay is VAT and Shipping Admin fee which is about 12-15. Ask the seller to put low value on paper work and you'll pay minimum Vat.

A_Camera
21-04-2017, 09:46 AM
If this is a router then wouldn't use 2005, it will be far too slow. Router needs at least 10mm pitch and at this length I'd be inclined to use 20mm pitch with 2:1 ratio to lower screw speed and increase torque.

Should get 2020 screw with end bearings and machined for about 200.

You are probably right but I mentioned 2005 because 1605 was mentioned before, which I don't think is very good at that length due to the risk of deflation. 2005 is considerably stronger but of course 2010 will be even better speed vise. I didn't know that you can get 2020 but sure that would be even better at this length.

Paul3112
21-04-2017, 10:50 AM
If this is a router then wouldn't use 2005, it will be far too slow. Router needs at least 10mm pitch and at this length I'd be inclined to use 20mm pitch with 2:1 ratio to lower screw speed and increase torque.

Should get 2020 screw with end bearings and machined for about 200.

Not arguing here, but from experience .. when using steppers, the faster the screw the greater the chance to miss steps. (tool load)
I will also ad this link as Fred now ships from Germany. https://www.aliexpress.com/store/product/Anti-Backlash-Ballscrew-RM1605-L1000mm-SFU1605-Ballnut-BK12-BF12-End-Support-1605-Nut-Housing-Bracket-6/314742_1639768705.html?spm=2114.12010612.0.0.PXFXn 5

davo453
21-04-2017, 11:35 AM
Thanks again.

I have costed this out (haven't asked for a quote though) and I am up around $600 ish (+VAT etc) so that kills the whole idea for the time being, cash flow is not so good right now.

The problem seems to be that the screws would need to be 1500mm long and at that length the shipping goes through the roof, so because of that using a local company such as Zapp might be cheaper anyway.

The machine does more that earn it's living so I'll save up the pennies over the next few months.

Cheers

Dave

A_Camera
21-04-2017, 09:59 PM
So, back at the original idea. Make some delrin nuts and off you go.

davo453
24-04-2017, 10:00 AM
So, back at the original idea. Make some delrin nuts and off you go.

As I said I have had those (for almost 3 years) and they are great but don't solve the slight problem of lash (resonant frequency) of the screw but it's not at all that bad really just a desire for my version of perfection I suppose. :05.18-flustered:

A_Camera
24-04-2017, 03:33 PM
As I said I have had those (for almost 3 years) and they are great but don't solve the slight problem of lash (resonant frequency) of the screw but it's not at all that bad really just a desire for my version of perfection I suppose. :05.18-flustered:

But if you make the nuts it can indeed solve the backlash issue. Not an optimal solution but definitely a solution. At least until you can afford balls crews.

njhussey
24-04-2017, 03:45 PM
But if you make the nuts it can indeed solve the backlash issue. Not an optimal solution but definitely a solution. At least until you can afford balls crews.
It's not a backlash problem I don't think from reading the thread, its whipping of the leadscrews because he's driving them past their max speed to get the speed he wants to machine his materials i.e. beyond the capabilities/limits of his machine. Belts, R&P or ballscrews are the only solution really to machine at the speeds he wants.

Alternatively slow the feed and also RPM of the spindle until there's no whipping......

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Boyan Silyavski
26-04-2017, 07:39 AM
600$???

The link i pointed you to is much cheaper.


Also maybe your design is not good. Meaning you drive the screw directly or belted? As when belted the screwis acual length, not the length of your machine. And as that could mean 20-30% longer than actual length necessary.../when screw is end driven directly/


Dont overthink it. Buy 2 screws you need as cheap as possible as you find them. Then you will upgrade rest at a later time. Accept that there is no other way and concentrate how to achieve the best result. All else is no better than what you have now.