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Drill press wobble?

lampwins

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Hi,

I have been working on a couple of practice kits and I wanted to try a few holes on a drill press. They turned out a bit… weird looking. I’m no machinist so I am not even sure what the proper terminology is in this case. Is this chuck/bit wobble? After noticing the results on one line, I changed to a brand new Cleveland #40 bit, with the same results. This is from a cheap Porter Cable drill press from Lowes. Any suggestions? Maybe chain the press to the hitch of my truck, drive around the block, and try again? Am I overthinking this?

Thanks,
John
 

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Thats not the chuck wobbling, that's just the "almost round" hole shape you typically get with a drill bit in thin aluminum.
 
Hi,

I have been working on a couple of practice kits and I wanted to try a few holes on a drill press. They turned out a bit… weird looking. I’m no machinist so I am not even sure what the proper terminology is in this case. Is this chuck/bit wobble? After noticing the results on one line, I changed to a brand new Cleveland #40 bit, with the same results. This is from a cheap Porter Cable drill press from Lowes. Any suggestions? Maybe chain the press to the hitch of my truck, drive around the block, and try again? Am I overthinking this?

Thanks,
John

This 3 lobe hole is typical of a standard drill bit in thin material. If you want it round, use a reamer to finish to size.
 
Properly drilling thin material is a challenge. You need to have high RPM about 2,000 and use very light feed rate.

For a perfect hole you may need to drill .005/.010 undersize and ream to size.

For all of the match drilling that I did on myRV-7A kit I reamed only no drilling. I
That created a nice round hole with minimal demurring.

You can buy #30 and #40 chucking reamers at Aircraft Tool Supply.
 
Thanks!

Thanks for the explanations, this makes much more sense to me now. I do have reamers so I will give that a try and hopefully learn a thing or two that sticks!
 
You might also try using a drill bit from a different vendor. Another possibility is that you're rpm is too low. Those small bits need more than a typical drill press can give them, so set it on the highest speed and don't bear down hard - go slightly light on the pressure.

Don't know if that'll help but it's worth a try.

Dave
RV-3B, empennage, wings and fuselage done. Engine, canopy and avionics in and working on the cowl.
 
Pretty sure the holes I drill on my old craigslist-purchased drill press are better than that. Try un-chucking the drill and re-chucking it a couple of times. Sometimes it doesn't square up in the 3 jaw chuck. Especially the smaller drills
 
If you’re not aware as I wasn’t cause I’m not a tool guy either is that you can remove the top and adjust the rpm of the drill by adjusting the belts in the compartment. Try to speed it up. My ryobi drill began with a very low rpm setting.
 
My drill press I had to remount the mandrel, but after that has been straight as an arrow. However I agree on thin material and low speeds, you won't get a nice hole, has to be thicker material. Drill a smaller hole, like one or two #'s up, and ream to final size. I also found that I got great results with a gator drill guide and my nova drill, used on my tail cone support bars for the VS, very easy to keep the drill at 90 degrees, and reamed a nice straight hole. Piece was too awkward to get in a drill press and clamped down correctly (I've found more of this then not in my building).
 

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While it's true that a standard drill bit doesn't drill a perfectly round hole, I didn't have any of the holes on my RV-7 look that out-of-round. You said you swapped bits, but have you tried swapping the drill? The vast majority of holes you'll drill will be with a hand-held drill, so see what happens with a different drill. If you get better results, then there's something going on with that drill press.

Reamers are definitely nice to have in your arsenal of tools, but make sure that your tool is working properly or you'll have a different set of problems with the reamer.

One more thing...as my junior high shop teacher told me, "Let the drill do the work, don't be in a hurry to force it through the material."
 
Drill speeds too low plus incorrect pressure can lead to the tri-lobe shape in sheet metal. It's because of the two cutting flutes and flex in the bit. It's impossible to avoid without using a reamer in sheet metal but you should be able to get better results than what you're getting.

The ideal speed for a 3/32" bit is somewhere around 9000-10000 rpm. A 1/8" bit is closer to 8000 rpm. Unless you have a high speed precision drill press you'll never come close to those numbers. You'll have to settle for max spindle speed.

As for pressure, it's a feel thing but you should be making a (nearly) continuous chip. if the bit is squeaking or making small or powdery chips, add more pressure. Too light is as bad as too heavy pressure here.

At 2000 rpm (the typical max for most small presses) you'll be plunging the bit somewhere around 6 inches per minute.

Drilling into a block of wood can help as well.
 
It is not typical to drill thin aluminum with a #40 or #30 and use a drill press.
As most have mentioned, higher drill speed is better on the small bits.
And reamers are the best.
 
I’ve also noticed more wobble when using the spring type drill stops. Thought I had some bent drill bits, but they ran true when the drill stop was removed. Started out always using the drill stops, now only using one if there is a reasonable chance of damaging the piece being drilled.
 
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