[30dayo]

I have a home-made CNC router, that I made for cutting balsa, plywood, Fr4, for R/C airplanes - works fine for these.
My spindle is a Dremel-type rotary tool.

I tried milling a pc board, using a 60° cutter.
This also works, but my setup is not accurate enough to make very fine traces, so I want to upgrade my machine..

I bought a 3/8x8x8" aluminum plate, mounted it on the MDF table, and now want to machine the surface to be flat.

I have ordered 2-flute 1/8" carbide end mills, and would like some guidance as to cutting parameters.

Thanks for any help,
Don

[Tom-AMS]

several things may impact how "flat" you're able to machine the tooing plate. first, how much end play (axial movement) does your Dremel-like spindle have? for example, measuring my Dremel, I get 0.011" which is way to much play for any serious expectation of a flat surface. However, assuming yours is 0.002" or less, the next concern is how well it is trammed to the table in both XZ and YZ planes. Also does moisture in the air, etc effect the MDF table's thickness/flatness? If the spindle is not perfectly trammed to the table, you will get a stepped surface. Next concert is how far the endmill sticks out of the spindle/chuck. Make it as short as possible, even if you must cut some off the back end of the end mill. When ordering endmills, you can get "stub" length, with short flutes. The less "stick-out" the less tool deflection. High speed steel endmills will often cut aluminum better than carbide, however, in this case, the rigidity of carbide is a plus. If you take 80% width of cut (0.100" step over) and 0.010" depth-of-cut (DOC) and your spindle has enough power at 6000 rpm, then try feeding 11 in/min. For 8000 rpm, try 15 ipm. 10k rpm, try 19 ipm. I recommend spaying it with WD40 or some other cutting lube, and /or blowing the chips off ... you don't want the aluminum to build up on the cutter, nor do you want to recut chips. I'd use a conventional cut direction. Its going to take a while to surface the entire plate... you may be able to rev the spindle rpm's even higher, and feed faster, however if the bearings in your spindle get hot and grow, the DOC may change; one side of the plate may be cut deeper than the other. My biggest concern would be spindle quality, power and rigidity. At 0.100 WOC, 0.010" DOC at 8k rpm / 15 ipm, figure about 3 watts. If your spindle has the power, you may want to make, buy, beg, borrow a mini-flycutter, with a high positive rake, honed-sharp HHS cutter, a 0.750" flycutter at 0.600" WOC, 0.010" DOC, 4k rpm / 23 ipm, would need about 23 watts. The surface finish would likely be smoother / flatter, bearing temps would be lower / more stable, and the time to machine would much less. hope this helps.
Respects,
Tom AMS-MotoMachine & Supply
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[Spk64]

Not sure what type of aluminum plate you purchased. If it is MIC6 then it should be pretty flat. Can you surface the MDF top then just attach the plate?
Although not sure what that will do to solve your previous problems.
Surfacing the MDF and then cutting your project should yield a flatter surface. You still have the issues the previous poster mentioned to review.


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[30dayo]

Tom,
Thanks so much for such a comprehensive answer.
I will investigate all the areas you mentioned.

The rotary tool specs are:
120V 1.2A = 144 Watts
RPM (no load) 10K - 30K RPM

My first step will be to map the profile of the plate.

I will post results as I find them.

Don

[30dayo]

Not sure what type of aluminum plate you purchased. If it is MIC6 then it should be pretty flat. Can you surface the MDF top then just attach the plate?
Although not sure what that will do to solve your previous problems.
Surfacing the MDF and then cutting your project should yield a flatter surface. You still have the issues the previous poster mentioned to review.
Sent from my iPad using Tapatalk HD

Thanks for your reply.

The MD table has a usable surface of 360 x 600 mm, and is fine for everything except small-trace PCBs.

The plate is not a tooling plate, as they are very expensive, and has a slight warp.

My plate is copied from the one on millpcbs.com.
It has leveling screws, to get it as level as possible, and has pins through the plate into the table, to keep aligned.
Because of this, the surface of the MDF is irrelevant.

Don

[elfrench]

You could use the traditional method of leveling using a surface plate, blueing, and scrapping.

[Spk64]

Big difference on the millpcbs.com plate is that it is a tool and jig plate which is flat.
If it were me I would rather have a flat surface to bolt to vs using set screws in MDF. They will constantly move.


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[30dayo]

You could use the traditional method of leveling using a surface plate, blueing, and scrapping.

I don't think that would work for me: I'm not that good a hand worker. ;-)

[30dayo]

Big difference on the millpcbs.com plate is that it is a tool and jig plate which is flat.
If it were me I would rather have a flat surface to bolt to vs using set screws in MDF. They will constantly move.
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I have epoxied short sections of steel rod into the MDF, so the setscrews will not dig into the MDF, and the plate is held in place by pins going through the plate into the MDF.

Edit:
The plate, not the MDF, is tapped for the set screws