I normally can get fairly good results using the better quality bamboo ply, but I’m currently cutting out some profiles in thin 1/8" sheet bamboo. It is not as fused/dense as the good ply and tearing out on the surface more than I want to see. Results are currently ‘okay’ but I want ‘best possible’ for a production scenario. I’m currently using a (sharp) Ø1/8 straight carbide bit. I know that a down-cut bit may perform better, especially when cutting deep, but my depth of cut in this case can be kept shallow. My speed/feed is conservative. I’ve divided my profile cuts into 2 toolpaths…the first path takes a couple of shallow skim passes (of .010"), and then the next toolpath profiles down normally to cut through the stock. That seems to have improved my edge just a little. And silly as this sounds, I’ve also tried to give the top surface a coat of shellac before the skim passes. I’m not sure if that has improved things or not but I would rather not have to apply finish during that stage. I’ve thought about stabilizing the bamboo first, but my tank is not wide enough to accommodate this stock size.
Any ideas on how to improve my top edge? Am I doing right by cutting shallow at first? How about, in general, using a higher speed and lower feed on those top surface passes? Are cutters made that are relieved on the bottom except for the outer corner? Or, should I run my chamfer toolpath using a V-cutter before I profile cut?? Or, first passes with an even smaller cutter? Any other ideas from the experienced would be appreciated. Would like to know what works best for most.
Thank you,
Kurt
A 1/4 compression bit could cut that in one pass, and would give both top and bottom good edges.
The trick is finding one with a short upcut section - I have had good results with the ‘Jenny’ bit.
Have you tried masking. The masking helps support the fibers. Some use oramask but a local source would be Walmart or Lowes for Easy Liner Adhesive Shelf paper.
The trick with masking is to lay it down from one side to the other to minimize air bubbles. Then use a J roller to roll it down for good adhesion. Just using your hand wont stick it down as well as a J roller.
If you can’t use a hard finish to bind the fibers, I like the mask idea, Guy.
When I was in the shop & we needed a nice crisp line cutting across end grain, we would score the line first with an Xacto knife or sharp point on a height gage. I wonder if running a drag knife around the profile before cutting would work??
A downcut endmill would probably work as well if you cross-cut every section of endgrain before making the cuts along the grain — alternately, why not a V carving tool to chamfer things?
Indeed, if you’re going to chamfer the edges Cody’s CNC (Cadence MFG) et.al. have downcut Vee bits.
Thanks for the link. I would need to (and may) try this compression bit to see results. I can understand that it would do better than a standard bit when making a full depth profile cut. It would reduce my overall machining time for sure, but would it eliminate surface tear-out completely (with my particularly fragile material)? Definitely worth a try though, thanks.
That is a good idea to try. I thought about trying blue tape but that gums up the cutter badly. If the shelf liner can be cut without fowling the bit, then my difficulty would be to remove it while not pulling out the fibers at the edge. Worth a try for sure, thanks.
I also thought about the drag knife. I agree that would most likely work but just an extra step (and purchase) for me. But if all else fails… Thanks
Even with the shallow cuts, I agree that a downcut EM would probably improve results over my straight cutter, although I like that my 1/8 router bit is relieved on the bottom. I really like Tod1d’s idea of using a downcut V-cutter. I think that will be a sure purchase for me.
Thanks all, for your input. All good ideas. Where I’m at this morning is to next try running a shallow ‘pre-chamfer’ around my part, using a V-bit (and soon a downcut V-bit). To me that seems like it should work very well by cutting the thin top layer of grain while it is still well supported by most all of the surrounding grain. Perhaps .010 deep, something like that. And then I can change to a normal bit (or downcut) to profile through and chamfer fully in the end. I have the thin bamboo laminated to MDF underneath so no worries with the bottom edge. I can accept the extra tool change and cut as a trade for not having to prep the surface with anything. Going for that… Thanks guys.
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