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jburks
04-15-2012, 01:11 PM
New to the form and have a question about masking a Vcarving. I'm using a brand new Bosch 90 degree carbide tipped Vbit cutting letters and numbers in MDF. The MDF was sealed and painted with 2 coats of latex before carving. The masking material I'm using is OraMask 813 fro signwarehouse.com and was applied very firmly by burnishing with a scrap of MDF leaving no bubbles.

The problem I'm having is the bit doesn't always cut the masking material cleanly leaving bits and fuzzies in certain places. It seems to always be where the bit exits the material. Most of the larger letters (1.5") cut pretty cleanly, but the smaller ones (.75") tend to have more of the exit remnants.

I've tried 10k rpm up to about 20k rpm with not much difference. I'm currently cutting at 100 inches per minute and haven't had a chance to vary that yet. So my question for those with experience is what would be the best combination of tool and feed speeds with this masking material to get clean cuts? Is there a better masking material I should consider? I've read about Dr. Crumley's Snake Oil Mask which sounds great for rougher materials, but I've also read that the OraMask is good for smooth surfaces.

Any suggestions would be greatly appreciated. Many thanks!

adprinter
04-15-2012, 02:25 PM
New to the form and have a question about masking a Vcarving. I'm using a brand new Bosch 90 degree carbide tipped Vbit cutting letters and numbers in MDF. The MDF was sealed and painted with 2 coats of latex before carving. The masking material I'm using is OraMask 813 fro signwarehouse.com and was applied very firmly by burnishing with a scrap of MDF leaving no bubbles.

The problem I'm having is the bit doesn't always cut the masking material cleanly leaving bits and fuzzies in certain places. It seems to always be where the bit exits the material. Most of the larger letters (1.5") cut pretty cleanly, but the smaller ones (.75") tend to have more of the exit remnants.

I've tried 10k rpm up to about 20k rpm with not much difference. I'm currently cutting at 100 inches per minute and haven't had a chance to vary that yet. So my question for those with experience is what would be the best combination of tool and feed speeds with this masking material to get clean cuts? Is there a better masking material I should consider? I've read about Dr. Crumley's Snake Oil Mask which sounds great for rougher materials, but I've also read that the OraMask is good for smooth surfaces.

Any suggestions would be greatly appreciated. Many thanks!

High speed feeds is always desired. However, experience has taught me that even though it may be machine driven, at the end of the day the same rules apply as hand driven: "Let the little Dog eat". I.E. the Router needs TIME to do it's thing (actually CUT the wood, not BEAT it!). Try slowing your feed rate down, and see what sort of results you get. (If you are running Mach3, no need to re-write the G code, just use the Manual Over ride, and set to maybe 30%). This will reduce the feed rate from 100 IPM to 30 IPM.

You will find, that keeping a log book of tooling types, speeds and feeds (and the material being cut) will help you to find your machine's "Sweet Spot" that works best for you. Hope this helps!

RossMosh
04-15-2012, 08:05 PM
30IPM is crawling. I wouldn't suggest that at all. In fact I'd say 100ipm is too slow. You're only talking about going 1/32 to 1/16" deep most of the time. As long as you have a good machine, you should be looking at closer to 200ipm to 300ipm. CNC V Groove Miter Fold & Signmaking Insert Router Bit by Amana Tool (http://www.amanatool.com/cncroutingdetails/rc-1028.html)

My guess is you're going too deep with the smaller letters. There is also a chance that your V-bit is not really great for v-carving signs. The bit simply might not be sharp enough to cut the mask cleanly. Last thing would be the masking (which is unlikely). Avery and Gerber also make options people like.

Last thing is, MDF is a weird material. You'd probably be best learning first with PVC, Corian, or something like that. You can get Corian scraps for next to nothing. You really don't need to mask Corian(you can just sand off the paint) but it's a good material to start with.

jburks
04-17-2012, 08:22 AM
I tried feed rates down to 20 ipm last night, and they all left some fuzzies. So I'm loking for a new bit at this point. I'll definitely be checking out all your suggestions and post an update here later. Many thanks to all!

jburks
05-08-2012, 10:32 AM
Finally had time last night to try out a couple of new bits. One was a CMT Orange and the other a Freud. Both were better than the Bosch but neither was perfect. The CMT seemed a little better than the Freud, but I think both were acceptable.

I tried feed rates of 100, 60, and 30 without much difference. As I said these letters are small, about 1" high or less, so there are small details but both bits left the island areas clean. There were a few small fuzzies, but they didn't seem to affect the finish much at all. The only cleanup I did before painting was to lightly brush the surface.

This was just a test piece and I'm also experimenting with the finish, but all in all a definite improvement. Not sure how much of this small v-carving I'll be doing, but it's nice to know it will work. Thanks for all the input!