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Spiral Milling Vs Drilling

I do a lot of spiral milling instead of drilling on my little high speed (RPM) mills. There are a couple reasons. One is it allows for fewer tool changes. I can point vent, dump vent, rough cavities and make the holes for pins and clamping screws all with the same little 1/8 SE end mill. The other is those little high speed spindles just aren't suitable for drilling. I've worked out a few operations I can drill with them, but they just aren't suited for it. It takes a lot of figuring and testing to find something that gets the speed, feed, and HP curve to all line up so it drills without smearing the drilling in the collet, wearing out the drill prematurely, breaking the mill, or causing lost steps. I am sure somebody has it all worked out, but that is not what I am asking.

Here is what I am asking. When I am spiral milling to drill holes I noticed at more than about 0.40 inches it starts making some noise that annoys my primordial hind brain. Since I work with a lot of 1/2" bar stock that leaves me finishing on the drill press among my other secondary operations. What causes that eerie noise, and what can I do about it? I am already blasting the area with water soluble flood coolant. If I could spiral mill all the way through it would save a fair amount of time in secondary operations. Often I have several molds to do the hand finish stuff on at once. Each half will have atleast two alignment pin holes, and anywhere from 2 to 20 clamping screw holes to be finished.

Reply to
Bob La Londe
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0.40" depth? How long are your flutes? are chips getting backed up in the hole? Or... have you tried changing spindle and/or step speeds? maybe something is getting resonant.
Reply to
rangerssuck

I do some of this on instrument panels. They are typically 1/8" thick aluminum, and the holes usually go all the way through. For small holes, I spot and drill. But, for holes over 1/4" diameter, I mill out all the holes and other panel cutouts with a 1/8" carbide end mill. Since this is on a 1J Bridgeport, my top speed without overspeeding the motor is ~2720 RPM. (pretty slow for carbide.) Anyway, I usually make the holes with 3 depth steps, so that is something like .050" step down in Z. I cut all the way through first, leaving .010" on the walls, and then finish to final diameter. Oh, and always climb cut! I do now have a routine for spiraling down, it is maybe a little faster, saving maybe a whole orbit or so per hole. I don't notice it having much difference in hole quality.

Jon

Reply to
Jon Elson

I suppose I could try breaking it up into two or three operation so the head raises and lowers giving the coolant stream a chance to hit the hole at different angles. I do hit the cutter fairly high so the spray shoots downward off of it.

I have not tried different speeds. I guess maybe a lower RPM with higher torque requirements could change something. Its worth a try.

Reply to
Bob La Londe

I suspect end mill deflection, which though slight, becomes ever more pronounced as depth increases, causing a sort of chatter due to the rubbing contact of the flutes. Might try stub end mills, and relieve the shank a bit behind the flutes.

Jon

Reply to
Jon Anderson

If chips are collecting in the bottom of the hole and being recycled into the cutter, you might try pilot drilling the hole through the part first so that the chips can be flushed away.

Reply to
Mark Storkamp

If chips are collecting in the bottom of the hole and being recycled into the cutter, you might try pilot drilling the hole through the part first so that the chips can be flushed away.

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On my big mill I spot drill and drill all the holes with its 5HP Leland motor driven 3600 rpm spindle. Its an awesome drilling machine. I have a hard time not getting good holes by drilling this way on that machine. Unfortunately the little 24000 RPM spindles (referenced in this thread) with just about zero useable torque below 12000 RPM just don't work out very well for me for drilling. They are awesome for higher feedrate tiny cutter milling, but drilling is a different animal.

No, moving parts from one machine to the other really isn't the answer either. Each machine has its own work to do. Often all 4 of my CNC mills are running at the same time. Sometimes even while I have the bandsaw cutting parts and I am turning something on one of the lathes.

Reply to
Bob La Londe

I suspect end mill deflection, which though slight, becomes ever more pronounced as depth increases, causing a sort of chatter due to the rubbing contact of the flutes. Might try stub end mills,

*** Unless you are using long reach end mills 1/8 inch shank anything pretty much is a stub end mill.

and relieve the shank a bit behind the flutes.

*** That is not at all a bad idea. I may have to look into that. Even a couple thousandths would probably do if deflection from rubbing is the issue.

Jon

Reply to
Bob La Londe

I've forgotten the name of the company, but there is an outfit that specializes in small end mills. They have stub end mills that have

-very- short flute lengths. Like maybe 1/8 for a 1/8" end mill.

Only other thing I could suggest would be to interp the hole small enough to leave enough material for a light finish pass, eliminating any chance of deflection. At the cost of increasing run time however. Giving this a try on a few holes though, might confirm or deny the deflection theory.

Jon

Reply to
Jon Anderson

Greetings Bob, Are you using carbide endmills? It sounds like you have a rigidity problem. .400 depth of cut for a 1/8 endmill is pretty long. Especially for HSS. I think what is happening is chatter. You can make things stiffer, slow the cutter, and increase the feed to help. Sometimes these options are not viable. But there are also cutter options. Carbide cutters are made in 1/8 diameter with 3 flutes that are not evenly spaced. This helps with resonant vibrations which I think is what you are experiencing. What size are the holes you are making? When spiral milling are you cutting a .125 slot? Is the hole diameter smaller than .25 so that the chips have somewhere to go? You may be having problems with chip evacuation which leads to chip recutting. Eric

Reply to
etpm

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