Major grief from a drill press

[digiex-chris]

I've got a fairly old but sturdy drill press. I do a lot of drilling for #8 taps, so I'm using the #29 drill a lot. I break drills that size all the time, even sharp new ones. Seems like every time I look at one of those drills, I snap it off in a hole. Thankfully most of the time I can get it out of the hole.

It seems to be breaking where it breaks through the hole, so it's grabbing coming out. On a drill that size I've got no feel on the drill press handle so I can't let up as it's coming out of the hole. Still, I'm breaking so many bits I'm suspecting either there's something majorly wrong with the drill press or it's setup, or my technique needs some major help. It was less rocket surgery to cut my valve seats than to drill 10 #29 holes! I need to buy #29's by the 100 pack to be happy! It's the only operation in my shop that reliably makes me swear. So far I've only been working on rebuilding a small commercial engine, I don't want to start destroying my own home built until I get this figured out.

Any tips? Any advice for looking into what might be wrong with the machine? Any technique tips? #29 is way bigger than some of the holes I've seen worked with here!

p.s. I drill this size and smaller on the lathe all day long without wearing out or breaking a bit. That little taig has way better feel though. I'm sure much better alignment too.

 

[cl350rr]

what speed are you running the drill press?

Have you checked spindle runout?

Randy

 

[digiex-chris]

I can only get it up to about 700RPM.

I havn't checked the runout. Should I remove the chuck and check the spindle directly?

 

[dvbydt]

What material are you drilling?

Ian

 

[digiex-chris]

1018 CRS. But that almost doesn't matter, I have problems with any steel or aluminum. Seemed to zip through cast iron with little problems but I rarely need to do that.

 

[arnoldb]

Ian beat me to it...
What material ? Brass, bronze and copper has a tendency to want to do that on break-through. CRS shouldn't want to rip through that badly.

If you use your hand to press the spindle up and down, how much play do you feel - or even better can you measure it?

I had to look it up; a #29 drill is a fairly big (in modeling terms) at over 3mm so you shouldn't be having problems with it - 700 RPM should be OK as well.

Can your drill's quill lock in position ? - you could try to slightly tighten it up and see if you get any better results - this is not ideal, but can be a way to stop things grabbing.

Regards, Arnold

 

[digiex-chris]

could I simply be pushing too hard? Or is runout a concern? I don't have a problem until I need to drill about 1/2" deep. If I touch a marker to the depth of the hole and let up pressure just before it breaks through, it seems less likely to break, but if I'm too light I don't form chips properly so I doubt I'm too heavy handed.

I can definitely do measurements, I'll do that when I get back home. I suppose chucked up drill rod runout is really waht we're concerned with...

 

[GailInNM]

I would suspect that the pinion driving the rack of the spindle down is worn. When you start to break out there is enough play vertically that the drill pulls the spindle down. Your #29 is probably in the sweet spot for this. Larger drill are stout enough to take the extra shock and small ones don't have enough force to take out the backlash.

Some, but not many, presses can be adjusted to move the pinion in closer to mesh with the rack, either by moving the pinion/handle or by shimming the rack. If the pinion is worn, replacing it is the best solution, but finding one may be a challenge.

Things that can help.

If the return spring on the quill is adjustable, tighten it up so there is more upward force. This will make it harder to pull the handle, but can move the "sweet spot".

Put an extra external return spring in the form of an extension spring on the quill housing to pull it up and keep the rack in contact with the pinion. Then you can remove it when it is not needed.

Lower the table so the return spring is wound up more as you have to move the handle more. This probably won't help much as the return springs are more or less a constant force spring that will not increase the upward pressure much.

Gail in NM

 

[dvbydt]

Try this test. Mount a DTI off of the column and onto the table. Press down with the drill spindle on the table. any movement above a few thou? If so, what might be happening is that as the drill breakes through, less pressure is needed but you have no control over this due to the "spring" wind up of the table.

Ian

 

[peatoluser]

Are you holding the work in a vice? or clamping on the table so the drill breaks through over one of the clearance holes?
when I drill brass or use small drills I try to arrange to clamp the work to a scrap piece of steel so the drill drills both pieces but use the depth stop so as not to break through the bottom piece. Can help with drilling brass. But if your breaking #29 drills regulary it sounds more like the machine than poor technique.
personaly I run that size drill at about 1000 rpm with brush applied cutting oil
yours
peter

 

[digiex-chris]

I knew this was the right place to ask! Got a big list of things to check. Worn out pinion seems likely, knowing the guy I got this thing from I know it was abused.

I clamp stuff in a drill press vice so it clears the vice. I'll try drilling into some sacrificial material, but sometimes the drill breaks nowhere near breaking through. Glad someone else thinks it's the machine too, since I can drill just fine with a tailstock on a lathe that uses a lever feed (taig's tailstock is nice for drilling).

I've only seen flex when using >0.5" drills, but I'll set up the indicator and check.

 

[bentprop]

You ARE using lubrication,aren't you Chris?At anything more than the drill diameter,I'd frequently clear the swarf,and do more of a "peck drilling"operation.But as you say,it may very well be the drill runout causing your grief.

 

[digiex-chris]

I tried a good cutting oil but didn't see enough benifit to keep using it on the drill press except on big holes or hard materials. Made more of a mess than it helped.

 

[kvom]

700 rpm seem pretty slow for that size drill, around 25 SFM. That said, since smaller drills work for you, you can predrill the hole with a smaller size and then enlarge with the #29.

 

[PaulG]

2X on too slow. Sounds like your doing production work. If so, you might consider purchasing a high speed drill press. I would be running a #29 around 1800rpm. On Aluminum 4000+.

 

[AllThumbs]

3X on too slow spindle speed. Also you should back the drill bit out a few times during the job to allow the chips to clear. Ease up the pressure just before breaking thru.

 

[Metal Butcher]

On my mill I have .050 + up and down play. Meaning a bad fit between the rack and pinon gear. When I'm drilling small diameters I press down just hard enough to take up the slack and allow the spring pressure to press down on the drill. The only times I have broken a drill bit was by pushing it too hard. With a small #29 drill bit Its hard to imagine the spring being overcome by the drill pulling the quill down. Its possible though, I guess. If your using a 'closed fist grip' on the ball handle try using two fingers only. You get a better feel that way. If your not pushing the bits too hard, then it could be a brittle batch of drills, if its only the one #29 size that keeps breaking.

I just remember a stupid experiment I did a few years back. I clamped a 1/2" x 1' x 4" (if I remember correctly) aluminum bar in the mill. I picked 10 drill bit starting with a #60 to #10 and pushed each one hard. It was more like a 'broaching operation' than a 'drilling operation'. It didn't take long, they didn't go very deep, and I broke each one! ;D

-MB

 

[jpeter]

Don't tighten the chuck so tight. Keep it a little loose so the drill can slip if it catches.

 

[digiex-chris]

not production work, I just seem to use drills in that range often, most of the holes I tap are approximately #8-32 sized. Anything larger than #29 drills I don't break, and everything smaller I do. Seems like that's the threshold.

I locked the quill and rocked the handle a bit, there's basically no perceivable play, so the pinion's ok. I didn't measure, but the spindle end play is WAY more obvious. I can lift the spindle up and down by 0.036". Only 0.005" runout measured on a piece of 1/2" drill rod right near the chuck. The pinion looks easily adjustable, I should dig into that top end and see if I can adjust that spindle bearing...

Does that sound like enough end play to be causing problems?

I'm missing a few step pulleys so I'm locked into RPM for now, maybe I'll deal with that and pay really close attention to rpm for drill bit sizes for a while and see if my luck improves.

It was my understanding that too slow was ok, as long as I was reducing pressure enough, just enough to keep making chips. that cutting speed for drills was a maximum for production purposes. Is that incorrect?

 

[dvbydt]

That endfloat looks like you found the answer.

Ian