I need help with leadscrew!!!

[DigiSoft]

Ok I am building small CNC. I have almost all parts exept the leadscrew. I am not able to build special leadscrew bolt but I have normal M8 bolt (it is 8mm or 0.31 inch in diameter) and it is long enough for my CNC. It is 1 mm or 0.039 inch betwean the leads. So can I use this as leadscrew? Would 1mm or 0.039 be to big resolution for the CNC?
Should I create special leadscrew with bigger leads for example 2mm or 0.078inch?
Thanks.

[BobF]

Many have built machines with just threaded rod or allthread ( I think you are describing M8 version). For a little more, you can buy ACME threaded rod, which will do a much better job. Not sure what may be available where you are.

[johnmac]

I built my first machine with allthread. It has 20 threads (turns) per inch. Has far greater resolution than needed and travels slow.

John

[DigiSoft]

Originally Posted by johnmac I built my first machine with allthread. It has 20 threads (turns) per inch. Has far greater resolution than needed and travels slow. John

Yes that is my worry, it will be slow. I am from Macedonia and it is little hard to buy ACME threaded rod. Well I don't know maby I'll use belt.
And what if I put gears to speed up the movement. I am thinking to fit one bigger gear for the stepper and smaller gear for the leadscrew. This will increase the speed but I don't know if the steeper would have the torque.

Thanks for the help!!!

[BobF]

Originally Posted by DigiSoft Yes that is my worry, it will be slow. I am from Macedonia and it is little hard to buy ACME threaded rod. Well I don't know maby I'll use belt. And what if I put gears to speed up the movement. I am thinking to fit one bigger gear for the stepper and smaller gear for the leadscrew. This will increase the speed but I don't know if the steeper would have the torque. Thanks for the help!!!

Lets assume you have to use allthread. Find a larger coarser version and see how low you can go on tpi (or high on lead). Maybe there is a reasonable compromise.
Don't know the size you are looking at for the machine, but there are ACME threads on things like clamps and bench vise screws, and of course you could cut one with access to a lathe. Be creative, maybe you can source some screws another way.

[johnmac]

If I was to build another machine using allthread, I would use 1/2 inch. Then I would buy a piece of Delrin plastic off of e-bay to tap out as the lead screw. I would split the threads so they could be squeezed together to reduce backlash.

Keep in mind this is building "on the cheap".

John

[DigiSoft]

wow thanks for the reply. I am not so worried about the backlash. I am worried about the speed. Well I'll go with allthreaded and see the resaults and if it is not good I can experiment with other leadscrew.

@BobF I was thinking alot about where I can scrape this ACME threads and there is no way I could find 40cm long threads from some tools or somethink like that. Well I was talking with my father and I think he could make one on his friend's lathe.

@johnmac when you say you would go with 1/2 inch allthread, did you mean the diameter of the leadscrew?

Right now I'll start building the CNC and I'll post pictures.

[teamtexas]

You can try to purchase a 1/2-10 leadscrew from Enco. They ship international and you can purchase on the web at www.use-enco.com. Look for this item number Model #NU408-0220. It works great. I purchased brass nuts from ebay that worked with it.

Dan

[johnmac]

Yes. 1/2 inch diameter. Coarse thread is 13 threads per inch.

Dan has a good idea with the Enco leadscrew. Take a look at www.dumpstercnc.com for nuts.

Don't ignore backlash when designing the x and y axis movements. It may be hard to reduce or remove it after the machine is finished. The z can be spring loaded if needed.

One other thing. If possible, don't waste time and money on a drawer slide design. Drawer slides are too "spongy".

John