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Drilling holes without shift

gaminn

Plastic
Joined
Mar 2, 2021
Hi,
I have a big and heavy 16mm steel plate with hundreds of 22 mm laser cut holes in it (welding table). I would like to make the holes bigger (24 mm) with my magnetic drill. The original holes are not of perfect cylindrical shape, they are rather conical (top diamater 22 mm, bottom diameter 22.3 mm) with quite rough surface. What tool should I use in order to achieve good surface finish and to maintain the position of the hole?

I tried an ordinary drill bit but it always shifts the hole by some small amount (e.g. 0.2 mm) and also the surface finish is not very good. The surface finish can be solved by using smaller drill bit and then a reamer in the second operation, but still there is the shift... And I would rather make the hole in one step as I have hundreds of holes to make.

I'm thinking about creating my own tool from e.g. reamer but that's quite expensive and I would like to get it right the first time.

Thanks for any advise

Martin
 
You might get away with a annular cutter if you are really careful. Not sure how you are going to pick up the existing holes. You made need to make a guide pin that you use to line up the mag drill and then swap to the annular cutter. The laser cut edges are going to play havoc on tooling regardless of what you do.
 
max 0.05 mm positional accuracy would be nice.

I'm thinking of some custom tool made e.g. from 3 or 4 flute drill bit. 3 stages grinded, first is just a little oversize of the original hole to center the tool in the hole, the second stage removes most of the material and the last stage is like a reamer - it finishes the hole and makes nice surface finish.
 

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Yes, the drill spindle of my 150 USD aliexpress mag drill has a lot of play and also the guides of the mag. drill are a little wobbly. I was thinking about elminating these factors with the custom tool which self-centers in the hole. Tried drilling 21.8 mm hole with 22 mm drill bit, even with my low quality mag drill I got nicely centered hole.
 
Yes, the drill spindle of my 150 USD aliexpress mag drill has a lot of play and also the guides of the mag. drill are a little wobbly. I was thinking about elminating these factors with the custom tool which self-centers in the hole. Tried drilling 21.8 mm hole with 22 mm drill bit, even with my low quality mag drill I got nicely centered hole.
If you are getting a 21.8mm hole in the centre, then you can grind a 21.8mm pilot on the 24mm drill and it will follow the centered hole.
 
A multi flute core drill might work, but it sounds like a horrible surface to be cutting, and you're not taking much out.
Have access to a machining center? Run a carbide end mill in a nice arc and mill the bore you want.
 
That's damn near impossible to do with a mag drill.
If the holes are laser cut, they should all be identical, so have a local tool resharp company grind a 3-4 flute 24mm drill that is the same form as the hole. That's probably your best bet. Aside from having it re-lasered or finding a cnc mill that can do it.
 
Could you get a carbide endmill, put a pilot on it, and have it ground so you use it as a drill perhaps. Done correctly, it would be like a multi-flute drill made of a material to handle the HAZ.

Edit, not thinking when I suggested an endmill, maybe start with a carbide drill and have a pilot ground on it to follow the existing hole.
This is a welding table I believe, and will still be a welding table. What ever hole spacing you've got now will be fine, just follow the existing holes.
It's a welding table.
Bob
 
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.2MM is pretty tight for a drilling tolerance especially when you are starting with an existing hole and one that is not perfect. I'd set this up in a big horizontal mill with a good readout and use an end mill to mill each hole.
 
If it's burned holes and a lot of them, and you are using HSS, plan on having multiple cutters on hand or doing a good bit of sharpening. Even low carbon steels can get some nasty hard skin from being plasma or laser cut. If you need accurate hole locations and don't have access to a milling machine big enough, maybe get a jig made with drill bushings and use that to do one line of holes at a time.
 
I know I'm operating in limited capacity....but I've never had good luck drilling out any existing hole and having it end up nice and round and in position, unless it's nice and round and in position to start with. Making a hole larger? Easy enough. Changing the true center of any hole? Pure end mill or annular cutter territory...no drill bits.
 
How about if you make a jig plate that pins to 3 of your existing holes, and has a drill bushing in a 4th hole? You won't be able to get to all of the holes, but after you drill out the ones you can get to, you can modify your jig plate to pin to the new sized holes and get the rest.

Or take the table top to a laser shop.

By the way, I've welded up hundreds of projects and none of them would have come out worse if a hole in the welding table didn't have a perfect surface finish. I wouldn't worry about the surface finish.

If someone gave me one of these new style welding tables full of holes I'd probably put a nice piece of plate over it. More my style. Think of how they build bridges or ships. Do you think they have fancy CNC'ed jigs? Pfah.

metalmagpie
 
Car reamer/Bridge reamer
reamer_car_fast_spiral_thumbnail.jpg
 








 
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