Ok, I need some straight answers about DIY milling machine!

[chola]

G'day all,

I'm going to attampt to build a cnc router / milling machine ovver the Christmas hols and need to know a few things. Any assistance would be greatly appreciated.

To start off with, I'll cover the basic stuff I know first.

Q: What do I want to do with it?
A: Machine small(ish) parts from alloy, delrin (not stainless, titanium etc), and also a small amount of work with wood (eg: routing names and designs into pine etc) - hobby type stuff.

Q: How big is going to be?
A: Table top size, so x axis probably around 2' long, y axis around 1' wide, height depending on power tool used.

Q: What will it be made out of?
A: A combination of timber and alloy (used where structural rigidity requires), and skate bearings etc, you know, the usual recipe for one of these.

Q: What's the budget?
A: Havn't really set one, but it is a hobby machine so I'm not going over the top! Having said that, I'm not really keen on spending $300 AUD on the actual router / laminate trimmer alone for my first project!


Now for the questions you guys can hopefully help me with!

Q: For what I want to do with it, which would be the better option? Wood router or laminate trimmer (not going down the Dremel path as have some doubts about 'play' in the spindle etc). Bearing in mind the availability of tools to rout wood and mill alloy (and price).

Q: Either way I want to get a machine with variable speed, however from what I understand even the lowest speeds on these two are still too fast for certain milling ops. Is there some electronics (PWM speed controller??) that can be wired up to lower it?

Q: What are the preferred speed ranges for cutting alloy as opposed to wood? The parts I am making are for large scale model cars, but even so are still relatively small compared to a lot of the jobs I see being done on this website. A lot of my cuts will be for small / fine details in the alloy (eg: imagine a brake caliper assemly from a formula 1 car, then take it down to 1/12 the scale, now you have some idea what I need to achieve), so the main focus is not on removing huge amounts of material in a few passes.

Q: Can I have the best of both worlds??? Can a machine that cuts alloys with nice fine details, be used to cut out peoples names in lengths of timber (axis size permitting of course). Or does the machine need to be built and optimized for a particular type of material?

Sorry for the long list, I have done some searching but have not come up with any straighy answers. All help most welcome?

Thanks in advance

[Madclicker]

If I needed to mill alloy (other than Al) I would convert an already capable mill.

Unless you want to build something just to play with I wouldn't build it around a laminate trimmer.

I don't think you can have the best of both worlds in one machine.

[chuckknigh]

It all comes down to precision and repeatability.

Notice I listed them separately...they're not the same thing.

First, let's talk about the router. If you look on eBay, you'll find a seller who makes high quality spindles, with belt drive, and prices them very fairly. For wood work, and light milling in aluminum and brass, any wood router sould do fine...for significant amounts of precision metalworking you'll need a real spindle. It might even be cost effective for you to build 2 units...in the US, Harbor Freight sells a mini mill that is popular for conversions. All metal, with a built in (real) spindle...of OK quality.

As to lowering the speed of the router...of course you can do it. Again, Harbor Freight sells a router speed control which works quite well...but it also lowers the torque of the router, so for metalworking, it could create a problem.

Now...back to precision. For fine detail you'll need a very tight system with no play -- antibacklash parts are expensive, but easy to fabricate. Search on this forum and you'll find quite a few antibacklash nut designs, for all sorts of leadscrews.

Leadscrews -- the screw that drives the table. Do you have a vise/maul? If so, go outside and look at it -- the screw stays put, while the nut (and consequently the moving jaw) moves along its length. That's how these machines work -- just with higher precision.

Can you have the best of both worlds? Of course -- just be aware that it's going to cost you. High precision is fairly expensive...and expense is directly related to size. High precision ballscrews and linear slides are priced by the inch...think about it. Do you really need a high precision machine of that size, or do you need a high precision machine to make 2x2" parts, and a lower precision machine to make 2x2' parts?

-- Chuck Knight

[project5k]

chuck makes some really good points... sounds like you know about what you want to do with it, now you need to figure how precise you need to be... is .002" good enough or do you need .0001"... how much detail are you looking to have in your finished parts... and just how precise do they need to be.. for most wood stuff, i think .001" is WAY good enough... but for aluminimum, maby not so good, depending on what your making... personally i went with a real router motor.. a porter cable... but i got lucky and it was handed to me along with the following quote, "here, i thought this might be something you could use, so i got you one".... the other think to think about isjust how fast are you gonna wanna cut.... if your looking for super fast cuts and lightning fast rapids, get ready for some sticker shock, cause servo systems, both the motors and the electronics to support them, are not cheap... if your like me, and speed isnt as important as just getting it running reliably, and money is a real problem, then bipolar steppers might be a better choice... i picked up 3 500oz-in 4 wire bipolars on ebay for under $200 usd... im building my own drivers and computer interfaces, so im saving a bundle there... you might think about going with a kit.. i have heard that there are several good choices, they come with the drivers and motors, and i think some even come with the powersupply....

another thing to think about is leadscrews, just like chuck said, there are options here, if you wanna go fast and be accurate and repeatable, ground ballscrews are the way to go, but here again, the mechanic in Mad Max said it best, "Speed is just a question of money, how fast do you wanna go?"

my machine has a theoretical step size of .00025"... thats waw more accurate that i need... my original plan was to gear this system up to double the speed and half the accuracy... but that'll have to come later when more $$ is available....

my best advice, sit down, figure out what you want and what you can afford, and then start looking for the parts and stuff that you need.... but be realistic about what you want to do, vs, what you can afford.. oh, and keep on asking questions here, cause these people know thier stuff, i have learned so much from just sitting here and reading.... its a really amazing source of information...

[chola]

Thanks guys for all the info,

To answer a few more questions,

Buying an already capable mill is a little too expensive here (in Australia), maybe cheap on Ebay etc, but freight is the killer! And would take the fun out of building one! I'm looking forward to the experience as much as having built a machine at the end of it! It's not something I NEED to complete in a certain time frame, so as long as it takes really to get a decent result.

I've already got the electronics sorted (I will use the same as I have on my lathe, 280oz stepper motors from Keling, and driver kits from
www.oatleyelectronics.com).

Speed is not of a great concern, as most of my pieces will be something of 2" by 2" square (maximum size), with some going up to maybe 3.5", as Chuck rightly guessed, this is what I really need to do for now.

It may be, however, that I do forget about building one to do both the alloy and wood, and just concentrate on the alloy for now. Then begs the question, if I am to go down this path, I can obviously make the machine fairly small (and rigid and not at massive expense), but what would be better, router or trimmer. At this stage I think the router has it.

I've pretty well go the mechanics of it sorted (in my head at least -leadscrews, anti-backlash nuts etc).

Project5k, half your luck getting handed a router! I'll be looking for an Ebay special I think - just have to make sure it has variable speed control, should be able to find for well under $100 AUD.

I guess the bottom line is, I am happy to build the frame / table / gantry etc, a few times if required (trial and error: make it out of timber to start with to test the theory then replace with alloy), but I want to get the right machine for the job (router).

On this basis, what are the poreferred speeds to machining alloy?

Thanks again for all the good info.

COlin

[chuckknigh]

Well, you did say you needed it to be precise, and you had a budget.

The mini mill at Harbor Freight is about $300US if you wait for a good sale...not far off the price for a router, in your country, and even if you just used the spindle part of it, it'd be dollars ahead.

Anyway, it was just a suggestion.

Keep an eye open on eBay (even considering freight) for good deals on short sections of THK linear rail, and you'll end up with an amazingly smooth system for very little money. 6" and shorter rails are commonly available for only a few dollars, and would make your project SO much easier.

For the leadscrew, you could even use standard triangular thread hardware store threaded rod...it's pretty good quality, in short lengths. ACME is a definite step up...and ballscrews are the epitome of quality for lead screws.

Read the posts on this forum, and you'll start getting a better idea of what you need vs what you want...and how to achieve it. This site is a veritable font of information, and almost everyone here is willing to share.

-- Chuck Knight

[chola]

Touche Chuck....

I think I will concentrate on a small(ish) unit, and work on making it as rigid as possible. Seeing as I'm only machining small parts. I think to start with this will give me the most accurate machine. I like the small rail idea...will keep an eye out, saves making something from scratch, and they're guaranteed to work!

For the leadscrew I was going to use threaded rod (about 1/2" diameter), with a great idea given to me by another member (Dave Anderson), of making a small box, passing the rod through it, sealing the ends, then casting resin around it, this way should make it virtually backlash free! The beauty of this is the resin can be cast in any shape required for mounting / screw points etc.

So let's forget about milling wood for now (can always build another more suitable machine right!).

Thanks again for the suggestions..now I feel I am getting somewhere!

Colin

[Madclicker]

If you want to mill metal, it needs to be very rigid and if it's a diy project it will probably be small also. Wood cutting machines are more forgiving, but you will notice few large diy built wood cutters that are actually doing production.

[jcc3inc]

Sir,

Visit www.outbackmachineshop.com and see if he has posted his small CNC mill on his site! Otherwise, contact Jim and ask for pix of his machine.

Regards,
Jack C.