[tekno]

I joined the San Jose Techshop and they have a Shopbot. I have project that I want to vacuum form and so I plan on using the Shopbot to make the plug. I was told that I will need a Spiral downward ball nose Router Bit but I can’t find one. I posted the file in hope someone would be able to help tell me what type of bit I should use. I plan on using a rough pass and a final pass on carving it. I was thinking of using plywood for the plug.

Thanks

[louieatienza]

I really would rough this out with a straight bit, not a ballnose. It would take forever with a ballnose. You could however use the ballnose for the finish pass.

Check onsrud.com for downcut spiral ballnose bits.

[ger21]

I've never seen a downcut ballnose spiral bit. As Louie says, rough with a straight bit, and use a regular ballnose for the finish pass.

[tekno]

ok thanks - I'll post how it works out.

[atwooddon]

If you plan on cutting the plug all the way to the bottom, you will have to flip the plug over the cut the area under the vertical semi-circular area on one end.

I agree, roughing with an endmill then finish with a standard ball end should work fine. Not sure what kind of plywood you are planning on using, but MDF might provide a better finish. Plywood can get a bit 'splintery'. If you rotate the drawing 90 degrees so it lays flat on the CNC table, a single layer of 3/4" MDF or similar material would be thick enough.

Don

[tekno]

Hmm I didn't look at the file when I exported it from Autocad inventor. but the plug will be 20"W X 24"L X 7"H - the flat part will be the bottom of the plug and the round end will be the area that's 20" across. I was thinking of plywood because it was sturdier then MDF. Also I have another part that will be connected to the end to make a down spout area that will be doweled so that it can be pulled apart after the forming so that the plug can come out easier.

[tekno]

I've never seen a downcut ballnose spiral bit. As Louie says, rough with a straight bit, and use a regular ballnose for the finish pass.

I was hoping you could link the bit you recommend

[ger21]

You'll probably have clearance issues with something 7" high, but something like these:
Vortex Tool: Two Flute Upcut Ballnose Router Bits - Series 2200

Vortex Tool: Tapered Ballnose Spirals - Series 2200

I've never used either. I've never done anything that high, so I use 1/8" bits similar to the first that I get on Ebay.

If you're just cutting MDF, you can also use a Core Box bit.
Groove Forming - Round Nose Bits

[tekno]

when you say MDF do you mean plywood or the fiber board?

Thanks

You'll probably have clearance issues with something 7" high, but something like these:
Vortex Tool: Two Flute Upcut Ballnose Router Bits - Series 2200

Vortex Tool: Tapered Ballnose Spirals - Series 2200

I've never used either. I've never done anything that high, so I use 1/8" bits similar to the first that I get on Ebay.

If you're just cutting MDF, you can also use a Core Box bit.
Groove Forming - Round Nose Bits

[louieatienza]

I would say if the school has a decent enough CAM, it should have the tool holder/spindle modeled, then you could simulate the g-code to see if you'll crash the tool/tool holder. I think the biggest problem will be to get that inside fillet at the semicircular portion at the end; I'd be inclined to make that a separate piece and glue it on afterwards. Provided the machine has enough Z clearance it would be tight, but you should be able to machine this with a relatively short bit, since ihe collet just has to clear that short side angle. Even less so if you pre-machine the block to the right size first.

MDF - Medium Density Fiberboard...

[tekno]

the school has Cut3d - Im still having some problems with setting up the XY for cutting

[louieatienza]

the school has Cut3d - Im still having some problems with setting up the XY for cutting

I prefer to set x,y at material center, for stuff like this I think it's easiest.

[tekno]

thanks - I was wondering if I was going about it wrong.