26-01-2011 17:06

sanddrag

Re: pic: So, Andy Mark was sold out!

I'd like to know how you're holding the sprocket, or are you not cutting all the way through, or has the hold-down been removed already in this photo?

26-01-2011 19:58

Brandtlamonte

Re: pic: So, Andy Mark was sold out!

Since you have 3 mind loaning my team one? =p

26-01-2011 23:26

seannoseworthy

Re: pic: So, Andy Mark was sold out!

The stock is held down with the dogs you can see, once the tooth profile is cut there is about 10-20 thou of material left and at that point i removed the sprocket from the stock material and began filing.

26-01-2011 23:38

sanddrag

Re: pic: So, Andy Mark was sold out!

If you did the whole operation on a fixture plate, you could probably mill the bore, then drill and tap a hole in the fixture plate, then put a bolt with a fender washer in it, then cut through the entire outer profile. Just curious, what did you use in CAD for the tooth profile?

26-01-2011 23:53

Big Ideas

Re: pic: So, Andy Mark was sold out!

For flat pieces it's possible to hold the stock with double sided tape (thin like carpet tape) on a sacrificial subplate like MDF, HDF, or MDF with melemene. Or drill a few tooling holes and screw the stock down the the subplate. This way you can make your final thru cut and not have to file all of those perfectly machined teeth.

27-01-2011 00:20

artdutra04

Re: pic: So, Andy Mark was sold out!

Double-sided tape on MDF won't work if you intend to use coolant. I've also had issues with parts shifting slightly on non-coolant milling (engraving acrylic) when relying only on double-sided tape to hold the parts in place.

Using a fixture plate (as sandrag already mentioned) is the best method. Since all AM sprockets have the same "standard" Ø1.875" six hole pattern, just make a permanent fixture plate if you intend to mill a lot of sprockets.

I've milled 25p sprockets from the CAD models available on McMaster and/or SDP-SI. I've been meaning to create an equation-driven SolidWorks model where you can just edit the number of teeth in the equation and hit Rebuild to make any size sprocket you want (I did that with gears a few years ago), but downloading existing part models is easier...

27-01-2011 10:53

seannoseworthy

Re: pic: So, Andy Mark was sold out!

The fixture plate we used was already made and ready to go and because we are only making 2 -4 we did not bother drilling and tapping. The tooth profile was created using the Roller Chain Generator in Inventor. The .ipt file was then imported to mastercam X.

27-01-2011 11:08

Brandon Holley

Re: pic: So, Andy Mark was sold out!

Following the old saying of "Work smarter, not harder". Totally agree, CAD files are so easy to find on the net (Mcmaster + SDPSI) that it makes it completely painless.


Also ditto the fixture plate, it's how we make almost all of our flat plates on CNCs.

-Brando

27-01-2011 11:30

Big Kid

Re: pic: So, Andy Mark was sold out!

I was trying to do this on our team's 3 Axis CNC Mill, and I only managed to get one done right. The other attempts all seemed to have distorted pitch diameters. Any suggestions on how come this kept happening and any tips on how to fix it?

I used CAD files from McMaster, and I had the stock mounted to a mounting plate we made for the sprockets.

27-01-2011 11:54

James Tonthat

Re: pic: So, Andy Mark was sold out!

Just an FYI, one of the forum sponsors, Innovation First sells 35 plate sprockets.

http://www.vexrobotics.com/products/...sprockets.html