Building a CNC Milling Machine

[leotech]

Hi Everyone,
I am in the process of building a CNC milling machine. I have been very lucky in getting high precision linear rails. These are all in one, lead screw, linear THK rails with 2 pillow blocks each, and THK screw lead inside, NEMA 23 mount for stepper or servo. These used to be in semiconductor inspection equipment, all very heavy duty. Some of the units are listed at 0.000125" resolution. Many of these rail systems are 50+ lbs.
I'm planning on having the Y & Z Axis on a fixed gantry while the X-axis moves. just like a router table. I was planning on using some 8020 stuff to build up the gantry, double bracing all the points. Once I get that up and running, I plan on milling out some parts for the mill afterwards. Milling parts for the mill.
Everything will be running on some Gecko 320 and servo motors. I have all that and electronics up and running on the bench. All the servo motors can turn the lead screws and i can't stop it by hand.

My main question is the spindle. Since I plan on milling AL, plastics, maybe light steel, I'm a bit stumped in what I should do.

1. Use a Dewalt Router or some brand, put a metal milling bit and go to town on it. 10k-20k RPM, haven't bought it yet (Home Depot extended warranty?)
2. Build a servo to spindle, moderate to low speeds
3. Take apart a Sherline metal lathe, just for the head and mount that on my Z-axis. mount a servo motor to the spindle. also not high speed. I'm not using the Sherline since I have my 9x20.

When I do "mill", can I use a Router 10k-20k with a milling bit, 1/4" shank, end mill or ball mill, mist controller, will that work? This is in AL.


Thanks,

Curtis

[SpeedsCustom]

You typically use high speed for small end-mill, v's ball noses etc. The thicker you go the lower the RPM. I think 10-20 RPM is too fast. At least thats What I thought?...


Also, Look into a Taig spindle head , there cheap, easy too mount and would be pretty nice.


-Jason

[rowbare]

Sherline Industrial Products has some spindle cartridges available. I am not sure of the speed ratings for these though.

http://www.sherlinedirect.com/index....TOKEN=91522079

[leotech]

some of the HAAS machines have 10k-30k spindle speeds. Do they cut at those speeds? I was thinking of modeling after them. What would happen if I used a 15k spindle speed and cutting AL, small cuts? it should work right?

[sergizmo]

The Sherline spindle can go up to 10K RPM if the preload is backed off a bit.

They are light duty spindles though. Only two bearings (one on top, one below) that are pretty small. Quality but not intended for heavy cuts. Milling steel...probably not a good idea.

The blurb up top of the industrial products page says that some components have been "beefed up". I wonder if this applies to some of the spindles over the ones offered on the machines?

As for the router, most(all?) of those have too much runout for metal work. A Zoner made a precision small mill with a high quality router as the spindle but he re-surfaced the taper on a CNC lathe and made his own collets. Also, if you ever want to do steel, the RPM ranges are just too high. Plus you are restricted to very small cutters.

Serge

[digits]

The rpm you need is dependent on the cutting speed, cutter diameter and cutter configuration. On my machine, with a 6mm dia (~0.25") cutter in aluminium I cut at 1200mm/min (~48IPM) at about 5000 rpm. I can't however cut aluminium at all at above ~2000 rpm without a shed load of coolant - it just welds to the cutter otherwise.

In theory, you could run a 1/4" at 20,000 rpm if you can get your machine to run at 192IPM and it has enough rigidity/spindle power to take the cut. You would need a lot of coolant though.

Quite a lot of DIY builds use a Sieg X2 head which is good for ~4-5k rpm, which you could easily manage with a belt drive and a servo.

[sansbury]

A Haas or other modern VMC will go 10-20k and beyond. It will also cost more than your car and maybe your house and maybe weigh more than them too.

You haven't said what you want to want the machine to be capable of. Gantry designs are not as inherently rigid as a bed- or knee-mill configuration. It doesn't matter how good your leadscrews are if the frame bends under cutting forces. There is a reason why metalworking equipment frames are usually made out of cast iron.

[leotech]

All my axis are a "all in 1" design. Rails and leadscrew on a 3/4" to 1" thick AL blocks. All my framing is using 1/2" to 1" thick AL. Most of my material is free from dumpster diving, scrap material I find anywhere. Since my planned cutting area is 8"x16"x5", it's quite beefy.

The X axis is the bed, Y and Z are on the fixed gantry in the middle of the X-axis.

I'm mainly cutting AL and possible steel.

[sergizmo]

I sent an e-mail to Sherline about the industrial spindles. Specifically about the 6507 cartige spindle with ER-16 and if this was any beefier than standard Sherline spindles. The body is steel so it should be a little more rigid at least. I'll report back with the response.

Edit to add: If you are even going to approach 10K RPM, you need balanced tooling to get a good surface finish. This can be expensive. Unless you will be using 1/8" and smaller endmills all the time, why the need for such high RPM?

Also: It better be one solid gantry to even think about milling steel. The amount of force required to mill steel (even 1020 or free cutting) vs aluminum is a factor of three or more to one.

[philbur]

10 to 15,000 rpm with a 1/4" carbide cutter in 6061 aluminium alloy should be OK. The problem with routers is that they are not normally designed/built for the kind of continuous use they will see on a CNC machine. The cheaper ones have deep grove ball bearings with little or no preload so axial and radial play exists and they burn up quickly. Also the collet taper in the spindle can be "shall we say" a little rough and ready. The best place to go is on one of the CNC router forums and find out what the guys with the experience are using. I finally got a reasonable result with an Italian made ELU router, expensive though. There are good and bad routers for this application. I wouldn't recommend a "buy it and see" approach, I have a box full of bad ones.

Phil

Originally Posted by leotech Hi Everyone, I am in the process of building a CNC milling machine. I have been very lucky in getting high precision linear rails. These are all in one, lead screw, linear THK rails with 2 pillow blocks each, and THK screw lead inside, NEMA 23 mount for stepper or servo. These used to be in semiconductor inspection equipment, all very heavy duty. Some of the units are listed at 0.000125" resolution. Many of these rail systems are 50+ lbs. I'm planning on having the Y & Z Axis on a fixed gantry while the X-axis moves. just like a router table. I was planning on using some 8020 stuff to build up the gantry, double bracing all the points. Once I get that up and running, I plan on milling out some parts for the mill afterwards. Milling parts for the mill. Everything will be running on some Gecko 320 and servo motors. I have all that and electronics up and running on the bench. All the servo motors can turn the lead screws and i can't stop it by hand. My main question is the spindle. Since I plan on milling AL, plastics, maybe light steel, I'm a bit stumped in what I should do. 1. Use a Dewalt Router or some brand, put a metal milling bit and go to town on it. 10k-20k RPM, haven't bought it yet (Home Depot extended warranty?) 2. Build a servo to spindle, moderate to low speeds 3. Take apart a Sherline metal lathe, just for the head and mount that on my Z-axis. mount a servo motor to the spindle. also not high speed. I'm not using the Sherline since I have my 9x20. When I do "mill", can I use a Router 10k-20k with a milling bit, 1/4" shank, end mill or ball mill, mist controller, will that work? This is in AL. Thanks, Curtis

[Jason3]

I think the quality of the spindle and tooling will largely determine your results, and matching spindle RPM to feedrate to get the right chip load is important. If you're using 8020 for the structure, you will probably get the best results with a faster spindle, lighter cut and faster feeds.

Lately, I've been cutting 6061 using a 1/4" 2 flute carbide EM at 40,000 rpm & 160 ipm, just light cuts. It gives quite a nice surface finish and - some will reel in horror - I haven't been using any coolant at all.

Perhaps you could build it with a router or die grinder and do some work with it, then look at upgrading the spindle when you know what your needs are, or when you can't stand the noise any more

All the best for your build!

Regards,

Jason

[digits]

Originally Posted by Jason3 I think the quality of the spindle and tooling will largely determine your results, and matching spindle RPM to feedrate to get the right chip load is important. If you're using 8020 for the structure, you will probably get the best results with a faster spindle, lighter cut and faster feeds. Lately, I've been cutting 6061 using a 1/4" 2 flute carbide EM at 40,000 rpm & 160 ipm, just light cuts. It gives quite a nice surface finish and - some will reel in horror - I haven't been using any coolant at all. Perhaps you could build it with a router or die grinder and do some work with it, then look at upgrading the spindle when you know what your needs are, or when you can't stand the noise any more All the best for your build! Regards, Jason

Are your endmills coated at all - I would love to be able to run dry, but even at 5,000 rpm I am melting the chips and welding them to my TiN coated HSS tools!