[grem110]

Hi,
I'm a sophomore high school student looking for a mentor in the Bay Area, specifically the Peninusla. I'm designing+building my own CNC Mill, and would love to get advice on it as I go through the process. Any level of help is appreciated--even just going through my current build plan would help me a ton and also teach me more. I would love to also get experience in a machine shop and working with machines, be they manual or CNC. I know this is a long shot given my age, etc. but I appreciate any help you can give to me. If you can't help me directly but can refer me to others, that would be a great help as well.

Thanks,
Matthew

[awerby]

Why don't you share some information about your proposed machine here? I'm sure there are plenty of people who would be happy to give you advice about it, even if they can't come by in person. It's nice that you're interested in machinery at your age, but it's doubtful that any machine shop would be able to hire you at this point. You might think about getting involved with a local makerspace or a place like Techshop, which has a facility on the Peninsula: TechShop is America's 1st Nationwide Open-Access Public Workshop -- TechShop Menlo Park You can take classes there, or use their facilities to build your projects.

[grem110]

Ok--you commented on one of my posts about the CNC Mill, but here's its description again and a few questions I have regarding it.

The frame is going to be a fixed gantry made out of 2x2 8020. Looking at using THB6064 drivers with nema 23 270 oz-in steppers. "Spindle" is a Bosch 1617evs 2.25 hp router with precisebits collets. Hope to cut aluminum, wood, plastic, etc. but not steel. Thoughts?

What I'm really trying to figure out is how large my mill should be. I found a cheap 210mmx360mmx400mm SBR20 rail set, but I'm not sure if that's large enough. With the blocks shortening travel, the max travel distance becomes 110mmx260mmx300mm (because there are 2 50mm blocks, and they are centered on the ballnut, the ballnut can move maximum of the length-50mm-50mm). In inches, that's 4.3inx10.2x11.8. I would obviously use the 4.3in length for the z, would anyone recommend having the y or the x be larger?

Obviously, space is a personal preference based on needs, but am I going to constantly want a bigger machine?

In the way of finding a makerspace or Techshop, I've looked at both and they are hard to justify. Techshop is expensive for me and also requires that I have an adult supervisor (at least for classes), so that's effectively double the cost. The closest makerspace that I can think of is Noisebridge, and that's a very long commute by train or if someone drives me.

[awerby]

Okay, I remember that post now. It sounds like you've got a pretty good set of parts listed. The TB6064 chips, as was pointed out, seem to be a better bet than the older TB 6065s that people have so much trouble with. But find a good implementation; it looks like there might be one here: THB6064 MassMind Stepper Motor Driver Kit I haven't tried it, but at least they provide information in English, which should help.

I don't know what you're planning to make with your CNC, but those ballscrews and rails do sound a bit short. If your primary use is making jewelry, a tiny machine might be all you ever want, but if not, then yes, you'll probably want something larger, if you've got room for it. It's not really essential to use ballscrews on a build like this, and the cheapest ballscrews aren't as good as normal acme screws. As you point out, some of the travel gets eaten up by the blocks and nuts. Those round rails aren't a terrible choice if they're supported, but you'll have better results with aluminum if you find some profile rails instead. If you keep an eye on Ebay, you can probably come up with some that are somewhat longer for not much money. You don't say how you're building your frame, but aluminum extrusions are probably your best bet, because they tend to be flatter than steel, which will make mounting the rails easier. Check the induction on those motors; low is better. They should be plenty powerful enough to run a machine that's 2' x 3', and many people have built larger ones with motors that don't have any more holding torque than that. What sort of a shop have you got access to right now to put this thing together?

I hear you about the long commute, and it's too bad that Techshop is making you provide your own adult supervision. Noisebridge certainly is an interesting place, but it's mostly oriented towards electronic hacking, not metalwork. I guess the "makerspace" movement hasn't penetrated to the Peninsula much beyond Techshop, but there may be groups forming even now to start one near where you are - if you find one, you might get in on the ground floor.

[grem110]

I was planning on buying the kit from MassMind, they seem to be a pretty decent source (also provide SLAm and Linistepper drivers).

Your advice on the acme screws is interesting. If I do that, do I need anti-backlash nuts?

So if I end up with a 2' x 3' machine or probably something smaller, does your advice on the ballscrews still stand? And will I need to switch to a moving gantry with 1 or 2 screws?

There are 2 induction levels of the 270 oz-in motors, and I'm going with the lower one ( I think it was 1.6mH).

Sorry about forgetting the frame, it's primarily going to be 2"x2" extrusion.

In the way of a shop, I have my school's lab, which should have a router (I don't know its specs, I heard about it back in May when I barely knew what a router was). It will also definitely have a bandsaw that can cut aluminum (no more hacksawing!), 3D printer(s), I believe a drill press, possibly a table saw (don't think I'll need that). I'm also part of FIRST robotics, and have some connections to teams with well-equipped labs--my team mentor will also know more people.

Thanks for the advice! This is really helping me out.

Matthew

[awerby]

I was planning on buying the kit from MassMind, they seem to be a pretty decent source (also provide SLAm and Linistepper drivers).

Your advice on the acme screws is interesting. If I do that, do I need anti-backlash nuts?

[Not really. Anti-backlash nuts are spring-loaded against one side of the screw threads. That works okay until your cutting forces overpower the spring, at which point all the backlash is back, somewhat unpredictably. As long as your nuts fit the screw pretty well, backlash shouldn't be a big issue, at least for most things you're likely to be making with this machine.]

So if I end up with a 2' x 3' machine or probably something smaller, does your advice on the ballscrews still stand? And will I need to switch to a moving gantry with 1 or 2 screws?

[Yes, you still are better off with a good acme than a cheap ballscrew. In general, moving-table machines are more rigid than moving-gantry ones. Their major disadvantage is that they take up a bigger footprint. It's good to run the table on 2 screws rather than one; that avoids the "stuck drawer effect" when the table racks to one side or another. But this takes another screw, another driver, and another motor, slaved to the other X axis motor.]

There are 2 induction levels of the 270 oz-in motors, and I'm going with the lower one ( I think it was 1.6mH).

[That should be okay.]

Sorry about forgetting the frame, it's primarily going to be 2"x2" extrusion.

[If you go with a bigger machine, you might want to use beefier extrusions, especially in places where they aren't supported.]

In the way of a shop, I have my school's lab, which should have a router (I don't know its specs, I heard about it back in May when I barely knew what a router was). It will also definitely have a bandsaw that can cut aluminum (no more hacksawing!), 3D printer(s), I believe a drill press, possibly a table saw (don't think I'll need that).

[Actually, if you're making straight cuts, a table saw can do a better job on aluminum than a bandsaw. You need to use a blade with a lot of carbide teeth that have a negative rake (they tilt back a little, rather than forward). Blades like that are also good for plastics. But it's good to hear that you've got a shop of some sort; I thought the schools had mostly closed theirs down. The drill press will be the main tool you'll be using, though; you probably won't need the router. Laying out the hole locations for motor mounts, etc. is going to be the tricky part of this. Use blue DyKem fluid Dykem 80300 Steel Blue Layout Fluid, Brush-in-Cap (4oz): Amazon.com: Industrial & Scientific on your aluminum parts so that you can see your scribed marks, and be sure to center-punch your hole locations before drilling them.]

I'm also part of FIRST robotics, and have some connections to teams with well-equipped labs--my team mentor will also know more people.

Thanks for the advice! This is really helping me out.

Matthew

[That sounds like your best bet for getting access to metal-working equipment at this point. If you can get some robotics projects going and have some team support, you'll probably find a lot of opportunities to deal with metals. Just be sure to take responsibility for your own safety - come with your own safety glasses, don't use your hand as a vise, and if you have long hair, keep it away from spinning tools...]

[grem110]

Ok. Sounds good on the acme screws.
I like the idea of still having a moving table, but I think using 2 screws is out of my budget. I totally understand the logic behind it though. What is your opinion on the guy that build his own supported rails (Krazatchu Design Systems I was think of doing that for probably just the y (table) axis. It would let me use larger rails, easily mount to 8020, and save money.

Thanks for your advice on the tools, especially the table saw and DyKem fluid.

[awerby]

You mean this: Krazatchu Design Systems ? I suppose you could try it, but it might not work with all rails, especially if they're hardened. I like profile rails better, anyway. Here are some on Ebay from a seller in San Jose that seem about the right size for one of your axes - he's got at least 2 of them: IKO LWL 9B 355mm Linear Rail with 2 MLC9 C Lube Linear Way Chucks | eBay I'm not endorsing this particular seller, but it's an example of what you can find, especially if you're flexible about your dimensions.