Advise needed on zeroing micro mills

[stumpgrinder]

Hello all, very new to CNC. We just got our Shopbot Desktop a few weeks ago, and have been spending most of my time learning drawing programs to cut the parts I need. We also messed around with the sign making program just to familiarize ourselves with the basic functions of the machine. When we were making signs, zeroing the spiral bits and v bits were not a problem, but on my first part which was an instrument fretboard, I had to use a 0.023 end mill. When I went to zero the bit on the plate, the clip popped off crushing the mill end into the plate. I started thinking that even if it hadn't popped off, perhaps zeroing this way is too rough on these tiny mills? I ended up visually bringing the end mill to the material surface and zeroing, but I didn't get my desired depth. Just wondering what others are using to zero these tiny end mills? Thanks!

[Brady Watson]

When I went to zero the bit on the plate, the clip popped off crushing the mill end into the plate....!

As long as you can keep that clip attached & your wiring isn't all jacked up, there is no problem using tiny diameter bits. I just did a large run of mini 3D parts using .01" diameter ball end mills on the end of my 5hp Colombo. Below 1/16", you should make a few modifications to how ramping (VR) is handled to add a little more cushion & to reduce the speed at which the tool begins to move. 0.4 IPS is too fast for micro carving to start moving...

Read my Write Up (http://www.shopbotblog.com/index.php/2008/03/a-ramping-the-vr-command-and-how-to-tune-your-tool-for-maximum-performance/) about VR.

-B

[stumpgrinder]

Thanks Brady,

I think we will use an alligator clip attaching one end to the larger clip and the other to the bit. That should solve the problem of the clip popping off as the Z axis moves. I'll have to read and re read your write up about ramping, still too new at this! We tried a fretboard in cedar with the bit only taking 0.015 depth passes. I had trouble finding info on how much to take at a pass, but remember reading approx. half the diameter of the bit is a good place to start? Once I figure out this ramping stuff, it will be on to a real fretboard of ebony this weekend! Can't wait!

[Brady Watson]

Start out going easy. 50-100% of the bit depth is a good place to start. Keep in mind these tiny bits like lots of RPM. The software the material, the higher the RPM needs to be. If you are burning, slow it down.

What spindle/router did you get? What's max RPM?

-B

[stumpgrinder]

We got the standard porter cable router that has speeds from 10000 to 23000. The first pass we did on the cedar practice board was at 23000 and it came out great.

[dana_swift]

I have used small bits with good results on a PC router also. What I do on the ZZero is lift the plate during the first plunge so contact is made in the air just above the material, then I put the plate on the material for the second plunge when it is slow. That works and doesn't damage tiny bits.

Good luck!

Your profile does not have a location.. what part of the world are you in?

D

[Brady Watson]

Just to add a little to Dana's post - I always touch the plate to the bit before I run the C2 command to make sure input 1 lights up. This ensures that I am getting good contact. Sometimes on certain types of coated bits, it insulates the bit & that can cause zeroing to fail and broken bits.

Unless I am cutting exotic materials or really nasty stuff, coated bits don't really do much for 3D. There isn't enough heat generated to be useful. If you were cutting metal or composites, that's a different story. Wood? Save your cash.

-B

[dana_swift]

Amen Brady on test continuity before issuing C2. My problem has been broken wires, or poor contact between the lug and the aluminum plate. I have broken bits of several sizes when the contact was bad.. now its just part of the procedure!

D

[cr2]

Welcome Lauri, If you are not already using these ER collets, they are a vast improvement over the standard Porter Cable collets...well worth the investment:

http://www.precisebits.com/gateways/ColletsNutsHome.htm

[curtiss]

I put a small red dot on the "2" of the keyboard.

This helps to avoid typing C3 when you want to type C2....

C3 can be a real bummer sometimes when you don't want it... :mad:

[stumpgrinder]

Hi, we are located in New Hampshire. All very good info everyone. We have been using the non coated bits. I think the main problem was that the clip that came with the desktop is a little too big for the smaller bits, so we used a mini alligator clip and everything worked out great today on our test part. We did buy one of those collets for the 1/8 shanks. I think most of our cutting of parts will be with the smaller bits for the most part. One thing I did notice about my zero plate, is that it is not flat. It is cupped slightly. Should the zero plate be dead flat? I would assume it should be.

[bleeth]

Your plate should definitely be flat. They are rarely, if ever, perfect.

[Brady Watson]

...so we used a mini alligator clip and everything worked out great today on our test part.

...Should the zero plate be dead flat?


Don't be afraid to modify these tools to make them yours. It is a robot - always remember that it works for you, not the other way around.

Yes. The Zzero plate should be flat. But as Dave pointed out, they rarely are. You can 'true' the plate flat if you aren't too heavy handed by bending back the way it wants to go. It takes some finesse so that you don't mangle it, but it isn't too hard.

-B

[erik_f]

Not as easy as the zero plate, but you can chuck the bit up, bring your z just above the material, loosen the collet so the bit drops down to the material, then lower your z over the shank, until you are happy with how much shank is in the collet and then re-tighten your collet. I have had to do this on occasion for diffrent projects.

[stumpgrinder]

That's a good idea! Next time I miss place my mini alligator clip, I'll give it a try.

[stumpgrinder]

Here is the fret board we made. Thank you for all tips!

http://www.flickr.com/photos/67204997@N07/6118280774/in/photostream

[gc3]

Well done!!!