Thanks for this information. I have guests for the rest of the week and I’m not available but will return to the topic next week. Thanks
I believe the CNC’s resolution is 0.1 mm, which is 0.004”, so I would expect the CNC’s accuracy to be between 0.002”-0.004”. Of course, the hole diameters won’t stay that accurate, because it’s wood, which swells and shrinks unpredictably with the humidity, temperature, phase of the moon, etc., but they will start quite close to what he wants.
If I understand correctly, he wants a 1/4” dowel to fit closely but freely in the holes. Tight clearance for 1/4” bolts is 0.257”, free clearance is 0.266”. I routinely cut the latter with 1/4” end mills with fine results in plywoods, MDF, and softwoods. That assumes the dimensions of the dowels are accurate, which needs checking, because it’s wood. It would definitely be a good idea to try a range of hole diameters with those dowels to see what gives the best results.
@CLeininger, the rpm values I set in VCarve seem to transfer to the controller correctly, though it won’t show it until you actually run the code the first time. And I’ve manually lowered the settings to a speed well below 6000 rpm, though I didn’t then cut with it. (I was using an edge finder.) So he might be able to lower the speed down to something appropriate for drilling.
But I don’t recommend it. In fact, I think Charles’s recommendation, a 3/16” end mill with a spiral cut, is best.
@zackg, the concerns that lead us to not recommend drill bits aren’t the accuracy of placement or hole size, it’s heat buildup, especially if they’re being run way over usual drilling RPMs. We’ve had one fire on the CNC from repeated drilling.
In fact, no matter what you use, I would break the toolpath into several separate sections in separate files. Then you can check periodically how hot the tool is getting and let it cool down if necessary.
Yeah, 17/64s is 0.265, so it depends on how tight the fit needs to be, and will get heavily down to the shaft being used. I figured his .255 was kind of an arbitrary number. Maybe it’ll be better to use 1/4", and sand the shaft a bit as an option, I think we both agree that it’ll depend on a lot of variables.
Someone had brought up that twist drill bits don’t like the higher CNC speeds and tend to wander. By shortening the bit length, I found that to be a cheap way of greatly improving the result while sticking with cheap/easy to find tooling.
Do you know what plunge rate was used when there was problems doing drilling? My software always put out super-fast drill plunging rates, but it produced good results. I never had a problem with drilling heat & Al, bit Al is kind of it’s own animal. Milling heat yes, but not drilling. I never drilled enough wood to see the heat issue. I found drilling ran much cooler then milling, probably because the MMR was so much higher.
I also do like the idea of pausing and checking it, seems wise given the history of heat problems.
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