I have made a few round bowls and I am getting bad results in the end grain sections (between 10 - 12 o’clock and 4 - 6 o’clock). It seems to be burning the wood in these sections and leaves wood fibers that have to be sanded away. Am I running my bits too slow (IPM)? RPMs too low/high on the router? I am running 100 IPM and 17,000 RPM. Wood is maple. 1/4" Upcut bit.
An upcut bit will definitely result in the fibers on the top edge as shown, but I see what you mean about endgrain.
Have you tried sneaking up on the final pass on the edge and only taking off the tiniest amount in the finish pass? If your design software doesn’t support it, you can use the offset tool to make your outer profile cut a few thou larger than the final size, then run the final pass to tolerance.
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Maple is one of the worst words about burning. It is easy to burn maple if you are not moving fast enough. However you said you were running at 100 IPM with a 1/4" bit. Maple is very bad about fraying on the end grain. I have turned a lot of maple bowls in the lathe and they are the worst about the fuzzy end grain. So when turning on the lathe the only solution is very sharp tools, using a sharp scraper and then sanding, sanding, sanding. The nature of maple is the fibers go in many directions.
Just make sure your bit is sharp and maybe increase speed. You can just use the 10% increase in Carbide Motion to see if you can tame the tear out. I generally run at 18K RPM and seldom deviate. So maybe increase your RPM up a little with the IPM to see if it gets better. If your tool is dull nothing will help but getting another bit. You can simply run your finger against the cutting edge and if it feels sharp it is. If it does not feel sharp compare to another bit that you know is sharp.
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Yep,
Guy’s right about Maple, wonderful hard wood, once you’ve finished it.
Looks like you’ve got several depths of cut there, is the burning happening on the first pass or when the cutter goes round to the next deeper level?
If this was my piece I’d try leaving 0.5mm of stock on the roughing toolpaths and then come back for a full depth double finishing pass with my ‘still really sharp, only used for finishing’ compression cutter.
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Thank you for all of the recommendations. I had never really thought of doing a roughing pass at say .2 inches per pass and then running a final pass full depth and just taking the last fraction of an inch. I could see that cleaning things up a bit.
I am using the “Contour” toolpath and I don’t see a setting allowing me to offset a specified distance for a rough cut and then running another toolpath for the final bowl diameter. Do I have to create another vector that is slightly larger than my final dimension for the roughing toolpath?
Erm,
If you’re using Carbide Create we’ll have to ask others for help on that as I don’t know.
If you’re in Fusion then it’s stock to leave in the toolpath dialog.
Yes, you will have to create an offset in the design. Select the circle you want to offset, click the offset tool, put in the value .2 and select outside / right in the drop-down box and it will create another circle outside of the existing one. Then create your rough pass contour line from the new outside circle. That should definitely help clean up the edges.
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