Table jumps around when drilling with an end mill

I think I know what's happening, but I'd like people's take on this:
I was drilling six 5/16" holes (in a line, spaced 0.4037" apart),
carefully centering the Millrite spindle over the crossed layout lines,
and drilling using a two-flute 5/16" endmill held in a 3/8" R-8 collet,
with the workpiece (mild steel) held in the mill vice, and black sulfur
oil brushed on as the lubricant/coolant. The table X and Y ways are
clamped, and the quill is moved manually to drive the endmill into the
work. As drilling proceeded, I continually brushed the chips away and
replenished the oil.
For most of the holes, it was slow, but no drama and the holes ended up
where they belonged.
For two holes, the table jumped around visibly, and the holes ended up
displaced.
The holes are all a tight fit on a 5/16" drill rod, but there are signs
of galling in the bores of a few. The endmill is undamaged, and still
quite sharp.
My theory is that a chip managed to get in between the side of the mill
and the wall of the bore and welded to the wall, only to be torn loose a
short while later, and that this is what generated the large forces
needed to throw the machine table around. The hole sometimes ended up
displaced because the table ended up somewhere else from intended. This
would be more likely near the beginning of the drilling operation than
the end, and the more wall there is, the more constrained the table is
by the stubbly little endmill captured by the hole it just made.
I suspect that a 1/4" twist drill followed by boring to 5/16" may be
faster and more reliable, and less dramatic.
Comments?
Joe Gwinn
Reply to
Joseph Gwinn
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you nailed it on the head. end mills really aren't designed for drilling. even ones that say "center cutting" will wind up pinching a chip between the face or wall of the bore and the mill. only takes 1-2 thou to set that galling and vibration up. better to have just drilled them out without a mill, but otherwise, yes use a drill to get some clearance and then finish with the mill so you have less chance of the chip loading.
Reply to
joel
A few thoughts come to mind. You might want a four flute for that, as a two flute generally is better for aluminum and other lighter materials. (Two flutes just aren't as rigid, and also wear faster, and generally have a more radical rake meant for softer material). Second, did you consistently dial the table to remove the backlash? Sometimes people inadvertently dial back a little to locate the cutting tool where they want it, but you have to do a final approach it in the same direction each time so the table's pressure on the feed screw isn't just "free floating". You may also be developing a little bit of play in the spindle, too, but that may be for a couple of reasons that I won't go into. Lastly, I don't know that I would do that in one pass, as you pointed out, a pilot hole is always a good idea, and putting the wear on a center drill and drill (something you can sharpen yourself) is a LOT less expensive than sending out your endmills to the tool grinder. It's not always easy to tell if your endmill is sharp, signs of galling in the bore really is a huge indication that it needs to be sharpened because it's probably the hollow-ground secondary peak possibly starting to drag- that means your primary edge is toast.
Reply to
Eli_S
Oh, and you can't put a 5/16 shank in a 3/8 collet, you might get away with a 1/64 difference but even that's not real great. If you did that, that is probably a large part of what the problem is and your collet is probably not real happy now either.
Reply to
Eli_S
[snipp]
Lesson learned (?): 1.) Facemills aren't good for drilling, because they cut on the side too. 2.) Your spindle needs an overhaul before doing 1.) again.
Nick
Reply to
Nick Mueller
Two things make me wonder about this:
1. You say it's worse at the start of the cut. It makes sense in that there is not as much wall to constrain the endmill at the start of the cut. At the start of the cut, however, there is also not much wall for the chip to weld to and throw the mill around.
2. Why would a drill bit be any better? The difference between an end mill and a drill bit is in the cutting end - the flutes and lands are just about the same. If it's chips welding to the side of the hole, they should be equally susceptible to it.
It's my guess that it's the cutting end that is doing the grabbing. Possibly due to chips welding on to the end mill itself, rather than the workpiece.
Try Aluma-Tap or another aluminum cutting fluid rather than threading oil. Run the cutter fast - a faster cutter has less time to overcome the inertia of the table. Use a drill bit instead. If you need a flat bottomed hole, start with a drill bit and finish up with an end mill. The drill bit could be full size, or slightly smaller. If nothing else works, you might try tightening up the quill locks so the end mill cannot pull the bit ahead as easily.
John Martin
Reply to
John Martin
No, the shank on the endmill is 3/8, and fits the collet perfectly.
Joe Gwinn
Reply to
Joseph Gwinn
That's my assumption and impression. No measurement or careful observation made.
The drill bit is smaller than final size, has a conical point, and is intended for the purpose. The twist drill would be followed up with a boring head and bit to make the final bore.
It's certainly possible, and the endmill would soon destroy the evidence.
I'm thinking that a 1/4" twist drill for roughing followed by the same 5/16" endmill for the final pass might be the ticket, and be a lot quicker than a boring head (albeit less precise).
Why would aluma-tap be better in steel than black sulfur oil? I have some Tap-Free on hand; I could try this. Now that you mentione it, Tap-Free worked better for countersinking in my now-neglected floppy too-fast drill press.
Faster may well help, but I'd like to understand and eliminate the root cause.
I don't need the flat bottom. What I need is an accurately placed and sized through hole. This is a dry run before I try it in A2 or O1 steel. The workpiece will become a woodworking drill jig.
Thanks,
Joe Gwinn
Reply to
Joseph Gwinn
That should be an advantage in a rigid mill, I would think: the hole will go where the mill wants it to go, even if the hole becomes a bit larger. But these holes are tight on a 5/16" drill blank, so it can't be much.
Why? Chip welding happens even to new machines. Nor does the spindle on my machine seem all that loose. What moved was the table, not the spindle.
What I've found with this machine is not that things are worn, but that they are caked with hardened oil, which gets in the way in various ways.
Anyway, how does one measure the spindle play without special equipment?
Joe Gwinn
Reply to
Joseph Gwinn
[snip]
I have a few 4-flute mills that size, none center-cutting (if memory serves). But, as discussed before, roughing out with a 1/4" twist drill is probably a good idea.
I didn't dial it in at all, I put a conical-point Starrett edgefinder in the 1/2" R8 collet, centered it, and steered the table so the cone point is exactly over the crosshair. This is verified by carefully bringing the cone point down and kissing the workpiece, making a very small mark that landed exactly in the intersection of the two scribed lines.
The table is then clamped, and is not expected to move. Quite the contrary.
It's certainly possible in a machine made in 1965. How do I test this?
It looks and feels pretty sharp, but roughing with a twist drill seems like a real good idea.
Joe Gwinn
Reply to
Joseph Gwinn
"Joseph Gwinn" wrote in message > I don't need the flat bottom. What I need is an accurately placed and
Joe,
You are working way too hard for a drill jig. Make the jig from aluminum or Plexiglas and use drill guide bushings.
See McMaster Carr Pg.2530 to 2536
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Reply to
Roger Shoaf
In that case, spot with a center drill, through drill with a 19/64th drill and finish with a 5/16" straight reamer.
Reply to
jlevie
snip-
Chip welding isn't the problem, it's the symptom. The problem is that the volume of chip developed by drilling with an end mill is far greater than the volume of the flute that is available to discharge the chip. Further, the shape of the generated chip doesn't lend itself well to being discharged, so it tends to ball up instead. One flute will generally load faster than the others, and it isn't necessarily the same flute each time, although it can be. Solution? Don't drill with end mills. They are not intended to be used as drills, not even center cutting end mills, That feature is intended to allow the end mill to plunge to depth for a cut when it's not practical to move the cutter while feeding to depth.
Correct, or, when location, roundness and/or hole size isn't critical, a reamer will often serve well enough.
Chip loading is the cause. It may or may not be welding, and likely is not. In steel, if the chip welds, the condition is often met with a destroyed end mill.
Correct! If you insist on drilling with an end mill, providing a hole large enough to reconfigure the chip such that it is small enough and shaped properly to fit the available space allotted is always a good idea. The best idea is to not drill with an end mill. They often yield an oversized hole and ruin the part being drilled because of the issue of chip loading.
Lubrication in this instance helps prevent chip loading------so the type of lubricant would play a minor role in eliminating the problem-----but doing any job improperly is best addressed by doing it properly. Perfume on a stinky body is a poor alternative to a shower.
Don't drill with end mills and you've eliminated the root cause. End mills are not to be confused with drills, they are not the same critter, not by a long shot.
Harold
Reply to
Harold and Susan Vordos
Indeed. And not all 2 flutes do plunge drilling all that well, either. I (am not a machinist by any stretch of the imagination) will always drill at the least, a pilot hole to clear the web, then plunge. And seldom see any of my customers doing a straight plunge on anything harder than brass/bronze/alum without a similar pilot hole. Or a 2 flute known and designed for plunging. And if the pilot is big enough..even a 4 flute does a good job..perhaps even a better job than a 2 flute. Smaller chip load/tooth.
Gunner
Political Correctness
A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
Reply to
Gunner
I did think of this, but the holes are too close together for standard bushings to fit. Plexiglas isn't likely to stand up, so it would have to be aluminum.
Actually, the holes have to be pretty good for a press fit to be reliable, and have to be accurately located, so I might well have the same issues, only with a larger hole and a softer material.
The dry run isn't because A2 and O1 are so difficult to handle, it's because they are expensive so I want to learn on cheap stuff. I'm still learning this mil.
Joe Gwinn
Reply to
Joseph Gwinn
"Joseph Gwinn" wrote in message >
I have made a bunch of drilling jigs out of both plex and aluminum. For close holes you can use the thin walled bushings and for fit you can get knerled bushings or just use a dab of CA glue. If the holes are so close that even the thin walled bushings are no good, then still make the jig from aluminum or plex, but make the guide bushing from O1 and press that into the plate.
Trying to make the whole jig out of steel also has disadvantages. First you have a large plate to heat treat, so DIY with a torch is not going to happen, and when you eventually get wear in the holes, you are facing an expensive repair, whereas if you use bushings you remove the oversize hoes and replace only the worn components.
How close does the hole placement have to be? Your end product is going to be wood, and you are still using a drill bit to make the hole. If the design calls for a +-.005 placement you are going to have big problems anyway.
Reply to
Roger Shoaf
Wrong concept! Repeat: A mill is bad for drilling, because it cuts on the side, a drill does not (except if you abuse it; we all did that). Also, a mill is not self centering, because he has a flat face, a drill has a conical face just for that purpose. As soon as one of the face cutting edges of a mill gets a bit more work, the mill (or the spindle) will bend and will cut on the side and he will be happily dig on that side until the deflection is too big for the cutting force. Then he will bounce back and try to catch the other side. :-) As gunner said, bore the hole (as big as possible) and then use the mill to drill if you need to. Abuse: If I need to make a bigger hole than I have a drill or a mill, I use a mill and feed quickly. That *guarantees* to make a bigger hole (and it *is* a hack). That's why they do ramping for milling slots and do not plunge mill the start. And if you need more passes, all are done in the same direction (preferably). Mills *do* bend under cutting forces.
If you want to locate holes precisely, start with a center drill (or better with a NC-starter drill, they are even better) and drill the hole with a drill. The drill will follow exactly where you started.
Not chip welding. Make a test and feed a face mill (drilling op) *fast*. You will notice that the mill tumbles. Even with the table clamped like mad.
Dial-indicator and some bar in a collet. Grab the bar and move it. The dial-indicator's tip is on the spindle nose or the collet holder (depending on your setup).
This discussion only reminds me, that I have to overhaul my spindle. :-)))
Nick
Reply to
Nick Mueller
Uh, 0.4037 apart?? have you actually measured this? You may be rudely surprised on the spacing using the equipment you have. Lot of good advice on this thread, however.
Reply to
Gordon
If it's any consolation I needed to counterbore a hole for a Socket headed cap screw this afternoon and used an endmill because I didn't have a counterbore ground up in that size. That jumped all around the place as well :-(.
PS The reason for needing the counterbore wasn't neat ness... I discovered, too late, that the head was occupying the space that a belt needed to go through :-(
Mark Rand RTFM
Reply to
Mark Rand
It's the theoretical center-to-center distance, used to compute the locations of the six holes, which locations are then rounded to the nearest thousandth. This way, errors don't accumulate.
Joe Gwinn
Reply to
Joseph Gwinn

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