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Drilling Tubing

J

johndib

Plastic
Joined
Apr 24, 2015
I drill 3/8" holes in 1" square tubing, 3/4" from the end and in the middle of the tube. I stack three high, two rows in the vice. Centerdrill the top two tubes to locate the 3/8" drill. After peck drilling, the top two tubes are perfect yet the bottom ones are off slightly. Is there a better drill or way to do this? It's as if the drill bit is walking. We used to do them one at a time in a milling machine manually and this has greatly sped the procedure up but I need to have the holes in the center. They're not off by a lot but enough that bothers me. I've measured the tubes and place them in the vice so that they're all the width but that hasn't helped. Advice?IMG_20160201_152251417.jpg
 
What kind of drill are you using? HSS is tough and flexible, carbide is very hard and brittle so carbide might stay straighter and you wouldn't need to center/spot. But any loss of rigidity could shatter it and they're expensive.
 
Only the top hole has a spot, so the drill is walking when it enters the upper and middle tube's inside walls. This can be compounded badly if the tubes are positioned with the welds up -- the drill is practically guaranteed to walk offline when it hits the weld.

Since you are drilling 3" deep, you are thereby using a long drill, which will even more easily dive offline.

Can you drill the top of the upper tube, then go in with a 5/16" spotting drill to spot the next entry? The final entry would be down 2", so even a spotting drill is likely to walk down there. Maybe a carbide one.

If the bottom tube is still wonky, you might try stacking 3 wide x 2 deep, but then you will need to be more careful with varying tube widths. Maybe put something a little compressible on the moving jaw, 60 durometer urethane maybe. Since you are only drilling, you don't need a gonzo grip.

Regards.

Mike

P.S. Ha ha, two other guys typed faster than I did :typing:
 
First thing I'd try would be a split point drill if you aren't already. The chisel point of a jobber tends to keep the drill from centering, especially if it's already got some runout. Without the spot helping out the drill it walks a little per tube wall each time and that gets amplified the further through them you go.

We do a fair amount of holes in tubing as well and I've mostly given up drilling through from one side. For some of them we've just gone to bore/helix milling as it creates a rounder hole and the operator can tend to another machine while it's running (not doing thousands though of course).
 
A 118 included point will walk less than a 135, also use a slow twist with a shallow flute. A lot more rigid. I would not try carbide too likely to break from shock in your application.
 
You need to index the tube so your never drilling through the weld seam makes a big diffrence in something like that. These days i just use the shortest possible length drill and drill them one at a time, no spotting with a screw length drill and its fast, really fast.
 
As one suggested you may be better off with a carbide drill, you would want to still slow down and do light pecks at each tube wall until drill has started into material.

The tubes look thin wall, Im not so sure I wouldn't try a 3/8 long reach spotting drill and go all the way thru. With no flutes it would be way stiffer than a twist drill.
 
Here is another idea, not sure how it work out but..
What if you replaced the stop you have rigged up with on the has pins with drill guide holes in them that go up inside of the tubes.
As the drill passes through one tube to the next it is support by the drill guide (hardened bushing be best) that's inside the tube.
 
I'd probably drill thru undersized and follow thru with a 3/8 carbide endmill. It doesn't need to have 3" of flute. Just spin down the shank so it doesn't rub. Bonus is you should get a fairly burr free hole.
 
Skip the center drill, replace with a stub split point. Just long enough to go into the second tube. After that I would be tempted to switch to an extended shank center drill. The first 3 layers of metal would act like a drill bushing on the center drill, no flutes to f things up.
It your drill is wandering the upper holes may not be round, you can check that, and may not be in the correct location length wise.
 
I drill through a lot of tubing, the one thing that has worked for me is after you drill through the 1st wall rapid down to a little above the next wall and drill into it about .05 at a slow feedrate to get the drill started, then pick up your feedrate an finish the hole and repeat this through the rest of the tubes.It takes a little more programming but has worked good for me.
 
Sometimes you can create more problems for yourself than its worth.I cant see you getting consistent results when your loading 6 jobs.Firstly you have to load the welded seams at right angles to the holes,Secondly are the tubes square,if not your never going to get 6/6 for this method.And lastly is your clamp holding the 6jobs down,it appears to me its only clamping the back 3 jobs
 
Make a small fixture and lay the parts out horizontally. You can make a cheap fixture out of aluminum, dowel pins and swing clamps or use mitee bites. I would say you can drill through 1 part much faster and easier than stacking 3 parts at a time.

Second I think your parts may be moving because that tubing is most likely not flat and you may be getting a stack up issue.
 
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