Newbie- backlash threaded rod?

[K.J.Everest@blu]

Hi very 1st post so hope in right place.

I'm starting on the road to build a DIY CNC Machine. Have brought some rod and linear bearings for X and Z. X is a 1m wide and Z will be around 250-300mm. going to use M10 ? threaded rod for X,Y and M8 or M6 for Z. The Y axis will have to start with angle iron and bearings and gas pipe (will be 1.2m long will Hopfully change latter). Using 1.85 Nm (2.8 amps) Stepper motors and HobbyCNC board. max cutting size 6mm using kress 800 or 1050

1. Have seen some backlash ideas using delrin and springs does this work ok?
2. Have seen on some threads that the software can take some of this backlash out is this ture or not?
3. If this all works and hope it will, mainly will be wood but some light Aluminium work will be done what sort of tolerance on a 20 mm cut out +-1.0 mm ??? or better.
4. Last item should I use M12 on X,Y as over 1m in lenth, Stepper motors up to the task?.Any thoughts would help.

Thanks for reading.

Kevin

[edmond]

Hi Kevin

I used M12 on my Lionclaw router when I first built it, the length of the M12 leadscrew was 1750mm so it generated some hectic whip, max speed with the M12 rod was 16mm/sec.I also tried to use HDPE nuts with a spring in between the two but this made the nut very stiff.I eventually upgraded to 12mm trapezoidal spindle and used a homemade delrin nut that was tapped using a offcut of the trapezoidal spindle that was modified into a tap.The trapezoidal spindle works very well, the one I got has a 3mm pitch pitch helped me douple my speeds to 35mm/sec.Marchant Dice in the UK has a wide range of trapezoidal spindle.My machine has a tolerance of about +-0.2mm over 100mm so the trapezoidal spindle is accurate.You could use M12 threaded rod for the Z axis, im still using it for my Z axis and have no problems due to the short length of 400mm

I am using a hobbycnc board and their 2.15Nm(305oz/in) steppers so your 1.85Nm(262oz/in) steppers should work well.

Good luck with your build.

[K.J.Everest@blu]

Hi

Thanks for the replay. Have been looking, reading and, to start a lot to take in. But I hope and sounds like on the right track. Have bought a few bits from Marchant Dice very good service.(on Ebay so got some little bit cheaper). did you use delrin for the z axis and trapezoidal thread for Y?

Kevin

[edmond]

I used normal M12 threaded rod with a homemade HDPE 20mm thick nut on the Z axis and TR12 trapezoidal spindle on the X and Y with homemade 30mm thick delrin nuts.Also try not to use leadscrews that have too fine a pitch as they will be slow, the trapezoidal spindle I use has a 3mm pitch with a single start I think Marchant Dice stocks a two start 12mm dia trapezoidal spindle which has a pitch of 6mm this will give you faster rapid speeds will reducing rpm on the leadscrew thereby reducing whip.

Hope that helps

[K.J.Everest@blu]

Hi

Thanks for the other info. may be tr12/3mm as funds reaching a limit. Found some info on trapezoida end blocks, I have a friend that can turn down the bar to fit a bearing. Held on end with C clip and the other?. That will be fun geting the mesurment correct. Been waiting 2 1/2 weeks for my Hobby CNC board to arrive and still not here. Still collecting items before starting the build. As spent my money on 30 mm bar for X with linear bearing. 20 mm for Z. And from looking on the internet think should have used angle iron bearings, as some great results. and spent money on thread. Spent a month looking before starting to buy. always the way, find a better way after you started or spent the money. Away thanks for the info.

Kevin

[edmond]

Hi

I used Aluminium Angle to make the X and Y linear bearings which use skateboard bearings running on black iron gas pipe, this sytem works extremely well and is also cheap to make.The proper linear bearings are very pricey here in SA so I only used them on the Z axis which uses 20mm rod and 20mm circlip groove linear bearings which were purchased online from vxb bearings www.vxb.com My hobbycnc board took 4 weeks to arrive so its the norm to wait a bit but its an excellent driver board for its price.

[K.J.Everest@blu]

Have checked this morning and board still with customs been there 5 days so far. Have been looking into the thread issue. due to the price of delrin over here. 41mm X 1m 30 pounds+,can buy three delrin nuts for about 20 pounds. You say you can TAP delrin with a tappered threaded rod. Looked at some taps for tr12/3 and over 200 pounds. Found a set on ebay less than 20 pounds but left hand. And the machining part of the thread, Not sure if th lath would be up to to that tolorance. The angle has one big advantage over my 30mm bar as far as I can see, Thats the load that can be supported,looking at a kress 800 or 1050 (2.5kg) was going for a 1/2 router but there over 3.5 Kg (more like 5+Kg), so not sure on the load. When all my item turn over the next week or so will have to get the dail gauge out.
Any way thanks for all the info. Back to work later this week so less time for my new hobby.

Kevin

[edmond]

Try and get some delrin offcuts from your local engineering plastics supplier.You can make a homemade tap by putting a taper on a offcut piece of trapezoidal rod eith a lathe and then grinding flutes along its side thats what i did except I used a bench grinder to grind a taper on the offcut it works extremely well.I would definitely support the linear bearing rod else you will have some major flex issues.Do a search on cnczone about the homemade tap.