another CNC emergency!!

[kbillan]

Been a while since i have posted here. I hope all is well!

Truth is that i have not used my mill much since the project i bought it for was complete.

Anyway, i have decided to revisit the project now that i physically have a copy of the part i was creating from drawings.

Pictured here at the bottom, is the original part, in white is my latest cut of the buckle, and at the top is my 1st attempt at it- which was done from pictures..




You can see that my newest cut (white) was drawn to the same specs as the original (bottom). But this is the story of my milling life--- it just doesnt seem to be cutting correctly. It tapers the edges, loosing left to right and top to bottom dimension, in addition to just not being to the correct scale everywhere else..


WHAT IS CAUSING THIS> LMAO????

hope someone can help.

I am using a Taig, with a gecko G540 (if i remember correctly) running it around 35 IPM and cutting in wax.


thanks in advance!

[Jeff-Birt]

What is tapered? Can't tell from the picture.

[kbillan]

if you look closely at the outer edges, it is cut tapered, instead of perpendicular to the bottom/back. This is because the machine is hitting the object with the shank of the tool. I was using a .0325 end mill for my finishing pass-- it has a .125 shank.

the roughing pass is done with a .125 ball mill, and it cuts the thing to the proper size.

this is quite frustrating! I always thought my original part was just not right, aside from being a bit too big.. but its not like my drawing.. and now i can see why.

[Jeff-Birt]

So you need a longer tool? I have some 0.0625" endmills with a 0.5" DOC would that work?

[kbillan]

you think that would fix it? Just a long reach end mill? what about the scaling issues? that, i assume is just a setting that is off somewhere?

you dont have anything smaller than .0625? Some of the details in the face didnt come out as crisp when i used .0625....

i bought 2 long reach endmills from microcut usa, 75.00 worth.. both broke within minutes.. cutting WAX...




Keith

[Jeff-Birt]

The scaling issue may be because your steps per inch are off. With a Taig and 200 step/rev motors and a G540 your steps per unit should be 40000.

I also sent you a PM about the bits.

[escott76]

Originally Posted by kbillan you think that would fix it? Just a long reach end mill? what about the scaling issues? that, i assume is just a setting that is off somewhere? you dont have anything smaller than .0625? Some of the details in the face didnt come out as crisp when i used .0625.... i bought 2 long reach endmills from microcut usa, 75.00 worth.. both broke within minutes.. cutting WAX... Keith

I use a .0625 2 flute .375 LOC square end a lot for finishing in Delrin. I also use a similar ball end with a lower LOC. If you are breaking end mills like this in wax you are pushing too hard. Lower your depth of cut per pass, and lower your feed. When working with small mills like this you have to take it easy. It's not spindle HP that's at issue, RPM may play a role, but if the bit starts to flex it's not far until it breaks.
Dunno what kind of CAM you are using, but if you have the capability rest machining can work wonders. Take out the majority of stock with bigger end mill, and then go back and clean up with the tiny guys, but ONLY the areas you couldn't reach. That way slow feeds and low DOC don't impact your times as much.
Another "crazy" idea is to see if you can split your part into multiple pieces while providing alignment holes. Slip a dowel pin through and presto, you are aligned. I do this sometimes with molds that are too deep to get into with a smaller shanked end mill. I did one the other day that was a mold for a mold (the male, which gets silicone poured in to make the female mold for production) where I did the shallow mold details on the surface of a piece of stock, then made a separate "ring" part to surround it, and provide an outer frame. Saved me having to cut all the fine detail at the bottom of a cavity where I really didn't have the reach with the fine tooling I was using. You could section your part, and do layers where you aren't dropping in past your flutes. Something to think about...

[kbillan]

Originally Posted by escott76 I use a .0625 2 flute .375 LOC square end a lot for finishing in Delrin. I also use a similar ball end with a lower LOC. If you are breaking end mills like this in wax you are pushing too hard. Lower your depth of cut per pass, and lower your feed. When working with small mills like this you have to take it easy. It's not spindle HP that's at issue, RPM may play a role, but if the bit starts to flex it's not far until it breaks. Dunno what kind of CAM you are using, but if you have the capability rest machining can work wonders. Take out the majority of stock with bigger end mill, and then go back and clean up with the tiny guys, but ONLY the areas you couldn't reach. That way slow feeds and low DOC don't impact your times as much. Another "crazy" idea is to see if you can split your part into multiple pieces while providing alignment holes. Slip a dowel pin through and presto, you are aligned. I do this sometimes with molds that are too deep to get into with a smaller shanked end mill. I did one the other day that was a mold for a mold (the male, which gets silicone poured in to make the female mold for production) where I did the shallow mold details on the surface of a piece of stock, then made a separate "ring" part to surround it, and provide an outer frame. Saved me having to cut all the fine detail at the bottom of a cavity where I really didn't have the reach with the fine tooling I was using. You could section your part, and do layers where you aren't dropping in past your flutes. Something to think about...

that sounds about bang on.

This buckle is the only piece that is a problem because it is about 1-1.5" deep. And like you said, i am making a cavity that sil is poured in. There are no details in the bottom of the cavity, but never the less- it is a deep cavity.

I afraid i just dont have the knowledge or training to do what you propose But it sounds awesome!

I think for the time being, i am going to try a long reach bit again- and then just take it way easy.

unfortunately- this project has sunk me, as i am a student LOL>. So i might be a few weeks until i can get to ordering a bit.

Thanks for your replies!
Keith

[escott76]

Originally Posted by kbillan that sounds about bang on. This buckle is the only piece that is a problem because it is about 1-1.5" deep. And like you said, i am making a cavity that sil is poured in. There are no details in the bottom of the cavity, but never the less- it is a deep cavity. I afraid i just dont have the knowledge or training to do what you propose But it sounds awesome! I think for the time being, i am going to try a long reach bit again- and then just take it way easy. unfortunately- this project has sunk me, as i am a student LOL>. So i might be a few weeks until i can get to ordering a bit. Thanks for your replies! Keith

A picture is worth a thousand words, but I'm at work at the moment. I'll try and show you what I mean later when I get back and can take a couple of shots of this. Again, dunno what software you are using, but once you have one model done of the part in question, doing what I suggest is really easy.

[Hokan]

It's nice to see another movie prop person on the board.

I'd brake your buckle down into 2 pieces. Basically the main buckle with the inner area dished out with a flat bottom/recess for the inner dial & alignment hole in the middle for the dial, and then the middle inner dial & drill it on the back for an alignment peg. Doing it that way should let you rough out and finish pass both pieces quickly and you'd have less areas on the silicone mold that would be thin/pointy down in the middle area that would break off when casting as the mold ages since you can cast it in 2 pieces.