I caught it on fire today. Lesson learned: use a drill bit instead of an end mill when drilling holes.
By the way when I was cleaning up, I noticed there’s a ground wire hanging down under the cable tray on the south side of the table that’s disconnected. Not sure if it’s supposed to be like that.
Wow, please be very very careful. A few other thoughts. Slow the bit/mill down to 1200 RPM by setting the Frequency to 20. Use an up-cut end bit/mill to clear the hole of chips. If you use an end mill choose a smaller one than the hole you need and run it around in a circular pattern. Finally plunge in multiple increments to clear the hole instead of one big plunge. Others, please correct me if I have misspoken.
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I believe all your comments are correct, Brian.
Using an end mill instead of a drill bit makes no difference if you are drilling holes that are the same diameter as the bit. When used this way, both create a large amount of heat, because the sides of the bit/mill are rubbing continuously against the sides of the hole.
Better to use an end mill to cut a pocket that’s slightly larger, which is likely the size you really wanted anyway.
Remember that you don’t want to cut a 1/4” hole for a 1/4” bolt (for example). I put charts around the shop with the proper clearance hole sizes listed for common bolts. If you are using a 1/4” hole, then you want to make a 0.266” diameter pocket with an end mill instead.
If you do actually want a 1/4” hole, say for a tight fit dowel, then I’d suggest using an 1/8” end mill to cut a 1/4” diameter pocket.
I wish we could disable the drilling toolpath as an option in VCarve.
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Using a drill bit on the CNC is fine as well. The issue most people have is not running the plunge speed of the drill bit fast enough, and slowing the bit down.
An 1/8" drill bit spinning at 8,000 rpms will drill just fine, if you plunge it fast enough say 125 ipms. And yes the bit will survive it.
If you prefer to slow the feed rate, you need to adjust the rpms accordingly. There is no reason to spin a drill at 18,000 rpms, and be plunge at say 40 ipm.
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You can use either drilling toolpaths or pocket toolpaths if you get the feeds and speeds right.
If you get those numbers wrong with a drilling toolpath, you’ll set the damn machine on fire.
If you get those numbers wrong with a smaller end mill and a pocket toolpath, you’ll just get a poor quality cut.
So I repeat, I believe that the average user should not use drilling toolpaths.
I’m using M3 screws, so i think the 1/8" size is probably appropriate. Looks like maybe I need brad point boring bits.
That is about right for a tight fit clearance hole. (3.5 mm would be the standard clearance hole size.) Smaller end mills are fragile, so you probably are stuck with using a drill toolpath.
The type of bit or mill you use won’t matter much regarding heat generation. People have set machine on fire with regular bits, brad-point bits, and end mills. You will have to get the machine speed and the feed rate correct, possibly with some pecking and pauses in the toolpath.
the other issue is that there are a limited number of collet sizes to choose from. a lot of the 115 bit set you just have to choose the closest. the 115 set is labeled in inch measure but a lot of the in-between bits will fit better in a metric collet.
technically, a collet set is supposed to be continuous, a collet can close on anything between its nominal size and the nominal size of the next smaller collet. but in my experience you take a big hit in holding force the further you go below a collet’s nominal value. thus the reason to check if a metric might be a better fit than inch (or vice versa)
the reduction in holding force is especially problematic because drilling is supposed to be done at lower rpm but higher torque than milling bits are generally used at. when a bit slips in the collet, it will generally ruin the collet. it will have worse holding force with any bit put in it, and can have significant runout.
when the bit slips, there is a danger of it pulling out and gouging the table, either while putting in a drill bit below the collet’s nominal size or later running with a damaged collet, even when using the exact size the collet was labeled for.
no big problem though, collets are replaceable.
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Thanks for the input regarding the collet size. I try to get 1/4" or 1/2" shank for all my bits. Due to the cost, most are 1/4".
Last night, I ordered the following to try:
Amana 201003
Amana 215003
Amana 217013
Dremel 631 brad point bits
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We have metric and imperial collets.
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