Elementary School teacher needing shopbot advice

[Tobias Sparks]

Hi, I'm a music teacher at an elementary school. We are building marimbas (big xylophones) for our students. Up to this point we've done most of the work by hand and are hoping to save our volunteered labor hours with the power of CNC!

We have access to a 5x10 shopbot at the local maker's space and I completed their basic one day training - which was quite skippy on info. I have played around on the machine and vcarve software and feel reasonably comfortable operating it.

I'm looking for recommended techniques (boring vs pocketing drill holes) and bit, speed and feed advice for the following cuts on 1 inch thick baltic birch plywood.

1. 1/8" Through holes

2. 3/8" Through holes and .5 in deep blind holes

3. 5/16" Through holes

3. 1/8" deep pockets with 3/16" corner radius

4. 1/2" deep pockets - smallest width 5/16"

5. 1" Through cuts

After CNCing, the part edges will be rounded over with a handheld trim router. For #5, (the 1" through cuts) we are hoping to get a very fine finish that doesn't require much if any sanding - maybe that's too much to ask for? If there are bits that work for several of our processes without needing changing that would certainly be helpful.

I'm attaching a couple pics of the instruments to give an idea. All the marimba keys are tuned by hand carving. We are hopping the CNC can take over the bulk of the work involved in making the frames.

Thank you in advance for sharing your knowledge,
Tobias Sparks
playmarimba.com

[coryatjohn]

What end mills are you planning on using?

[Tobias Sparks]

I'm looking for advice on what end mills to purchase and suggested speed / feed. Thanks!

[phil_o]

Where are you located? I am in Western, MA. I'd help if your not too far away.

Phil

[waynelocke]

If the CNC has a spindle I would run it at about 6000 rpm’s and use 1/8”, 5/16”, and 3/8” drill bits for the through holes. For the others, I would use bottom cutting endmills. 3/8” will give you 3/16” corners. You could probably do all of the pockets with a 1/4” bit and avoid some tool changes. Spiral the 1/4” tool for the 1” holes.

[Tobias Sparks]

Hi Phil, I'm in California - thanks for the offer!

[bbrozo]

I don't do much CNC work with plywood (usu. hardwoods & ponderosa pine), but based on the info. provided I would probably use 1/8" & 1/4" endmills to do the holes/pockets. The bits I have that would do most of this would be Magnate #'s 2101 & 2105. But, the 1/8" bit would only cut to a max. depth of 1/2". So, you might try Wayne's suggestion for drill bits for the 1/8" through holes. These bits I mention can be purchased from magnate.net. Also, Toolstoday.com has alot of CNC bits with supporting info. re: feeds/speeds. For example, see https://www.toolstoday.com/v-13779-46202-k.html.

Most importantly, do a test run on a plywood sample with the bits you've chosen before the final run.

And, California is a big state. I'm located in Camino, Ca. I'd suspect if you're near a maker space, you are either in SoCal or the Bay area - the latter isn't too far from me. I could help with this, if you want.

Bill

[chiloquinruss]

When I'm doing small parts and I know that at some point in time I will also be doing a round over, I use the attached bit doing a scribe ON the line of the part then cut the part. Works pretty good and saves some handling of small parts. A light cleanup is all it takes to finish off the pieces. When using Baltic birch plywood sharp bits work great. Listen to your machine it will 'tell' you when you've got speed/feed correct. Russ

http://www.talkshopbot.com/forum/attachment.php?attachmentid=33375&stc=1

[Tobias Sparks]

Thanks for everyone's suggestions. Bill, I'm in Santa Rosa - pretty far from you. Russ that is a cool bit, thanks for the tip. I'll start with drill bits and a 1/4" end mill. Next post will hopefully be a success story!