Homemade CNC questions

[ChaseLewis]

Trying to make a homemade positioning system for CNC and if it goes well might try my hand at 3D printing at a later time. However, need some insight from some more experienced people on some choices. My goal is to do wood and thin aluminum with this.

I have 3 questions but any extra insight is welcome.

1.
1/4 - 20 Right Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

K so I've been looking for linear screws and think this site online has the best deal I can find. Decided on 1/4" - 20 screw because it was cheaper then the 3/16" - 20 and has similar efficiency but can handle considerably larger loads.

Can someone give me some insight on how to pick my nut/flange setup? Plastic good or not worth it? I don't mind investing in brass nut/steel-flange but at $55 a piece They come out to nearly the same prices as my NEMA 23 425 oz-in motor a piece so that has me hesitant to buy at the moment because that doesn't seem right.

2.
Any place someone would recommend to get a linear rail system and what type would you all recommend? I'm shooting for a size of 2'x2'x1' and 3-axis, but think the ultimate size is determined by the price of the rail system.

3.
Not really a linear question but any recommendations for a router to use? i'm familiar with the electronics end, but the mechanical end is pretty new to me.

[ger21]

You need to use 1/2" acme screws. Anything smaller isn't strong enough and will whip like crazy. Also, you want 5 turns per inch or less....Definitely not 20!!

Check dumpsterCNC - anti-backlash solutions for home and industrial linear motion for nuts. They are preferred by most people here use. Plastic will work fine.

[ChaseLewis]

Thanks, was worried about whipping but have no experience for understanding what diameters are safe to use over what lengths. Actually price isn't that different for bigger diameters so that sounds good. Also I see the larger diameters plastic nuts have much more reasonable operating loads so that makes alot of sense.

Why do you want such a small thread per inch? Wear? Accuracy?

[ger21]

Speed.

[louieatienza]

To echo Gerry's comments, you'll have a wider range of useable speeds with the higher lead screws (lower TPI) given your stepper choice.

If you are using a router for a spindle, consider that even at low speed (10K-15K rpm) you have to move the tool at sufficient speed to prevent burning the work or excessively heating and wearing out your tool.

Looking at steppers with similar torque ratings, even past just 500 rpm the torque drops considerably. So if you used 20TPI leadscrew, that would equate to a torturous 25 IPM, with not much headroom. At that motor speed you'd then have to start worrying about screw whip, even with 1/2" leadscrews.

The "downside" is that with a multi-start leadscrew, you'll have a decrease in resolution, but, for most practical purposes, you'll still have plenty enough resolution.

[ChaseLewis]

Makes a lot of sense, thank you. I just noticed a lot of hobby machines used 3/8" so i thought I was safe.

Fortunately this morning I found 5/8" BallScrews for $9 a foot and new recirculating nuts for $19.99 so think I'm going to use those as its about what I was going to have to pay at the previous place for 1/2" ACME screws.

One more question.


Any good ideas for a linear system? Generally they seem expensive per foot, but still a bit confused on which option i should invest in.

I've seen some aluminum angle and v-bearings on a home-built that looked pretty good because it was cheap but was a bit worried about bending.

[louieatienza]

Makes a lot of sense, thank you. I just noticed a lot of hobby machines used 3/8" so i thought I was safe.

Fortunately this morning I found 5/8" BallScrews for $9 a foot and new recirculating nuts for $19.99 so think I'm going to use those as its about what I was going to have to pay at the previous place for 1/2" ACME screws.

One more question.


Any good ideas for a linear system? Generally they seem expensive per foot, but still a bit confused on which option i should invest in.

I've seen some aluminum angle and v-bearings on a home-built that looked pretty good because it was cheap but was a bit worried about bending.

I think for the money the 20mm rail from Glacern Tool would be your best best for anew purchase. It's getting increasingly difficult to buy NIB linear rail on eBay, unless you get them imported from China. You can also check out the CNC Router Parts system, which is a very good deal for the money.