First attempt at joints for torsion box

Hey everyone. I’m guessing this may be a tool bit problem. I created the inside holes at 18mm (for 18mm MDF) I actually didn’t expect them to fit with out Thor’s hammer. However they ended up 2mm larger. (20mm)

Everything else in every other direction seems fine though and only allows the smallest gap for glue.

I know I can probably get away with just setting the smaller (say 16mm) and then everything would fit snug.

This may sound dumb but just figured I’d ask.

Software used. (Autocad & elstcam)


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An endmill can have quite a runout/wobble, more in some occasions than others. Doing a testrun, measuring the actual cut compared to the CAM, and adjusting accordingly, would be the the most accurate solution. But I honestly seldom do it, because I’m too impatient!!

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Double check the tool diameter is set correctly in estlecam. I did that once and finally realized the diameter was mistyped… also check the tool in the collet. Make sure there is no debris in there which can cause similar problems.

If you need accurate cuts, you have to do a finishing pass.

Enabling a finishing pass means the roughing pass will stay a little further away. The full depth finishing pass will come by and only remove the 0.2mm you left in the roughing pass.

The fact that your hole is too big means the bit/machine is flexing into the cut. There is a setting for conventional/climb (and I always get them confused). Switching that should make it flex away from the work.

Also, the thickness of material is never perfect. So you need to be ready for some variance. Either measure the thickness, or make it a tight fit and then thin the tenons until they are a good fit.

Take measurements with a caliper or other precision measurement.

It’s odd for the tool to be off in one dimension and not both. Generally these things.are.circular at least.

If it is just one dimension, is the overall length of the part also off? Is is off by 10%, or is it a constant 2mm?

A 10% error is steps/mm (or 8%, etc…) a constant 2mm is something else.

Tool size diameter gets a “parts too large, holes too small” problem, or the opposite. Tabs and slots don’t fit together.

Belt stretch can give you a problem where things are too long in one dimension. That much is uncommon though.

Yeah its a constant 2mm only in the one direction. Ill check over everything. Im leaning towards bit size. When I got the router it came with a 5mm bit. (i just measured with a ruler) as i dont have calipers yet (there in the next amazon order) how ever by eye it looks to be 6mm. Ill run some test cuts and see what happens.

My eyes are 44 years old so it is possible to still be a 5mm bit :blush:

Thanks again Jeff. I’ll tripple check everything. Wanted to make this thing as easy to assemble as possible for any one to use for their torssion boxes

Hi Matt,
Thanks. I checked with a ruler and it seems to be a 6mm bit. (was packaged as 5mm)

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If all else fails ill try this. Thanks Turbinjorn

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So I guess it was a 6mm bit. Just done another test cut and came out perfect. Sorry for the dumb question guys.

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No problem, glad to help you solve the issue. That’s what is great about these forums. Any issue you may encounter, chances are someone has experienced it and we are more than happy to share the knowledge.

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