Using twist drill in magnetic drilling machine?

That depends. I suppose a adapter could be made for the ones built for rotabroaches. But normally you use a different type of mag drill that already has a chuck. Look at the Milwaukee line of mag drills and you'll see what I mean.

Wayne Cook Shamrock, TX

Thanks Wayne. I had a look at the Milwaukee range and I see what you mean. I've only ever seen the Rotabroach kind for sale in England, and I'd quite like to be able to use the Rotabroach cutters, so I was wondering if an adaptor was available? As you say, it might be possible to make one.

Presumably the kind of magnetic drilling machine which is built with a Jacobs chuck spins faster, so drilling with twist drills on the Rotabroach kind of machine might take a while? I don't mind that too much, though - most of the time my drill press is set on the lowest speed because the belts are so fiddly to change.

Chris

There are a variety of machines and ways to attack this problem. Smaller cutters are very fragile and so I have made up 7/16 drills to fit the rotabroach. If I remember correctly the shank of the cutters is 3/4 diameter. I would center drill a piece of cold finish about an inch long to match the 7/16 bit then braze a HSS drill bit in the sleeve. I would cut the bit in an abrasive chop saw since I only needed the end of the drill bit. If you are only drilling one or two standard sizes this is one approach. The lightest rotabroach mag drills will not accept the adaptation of a Jacobs chuck. The larger, heavier, and expensive magnetic base drills such as Milwaukee will operate either way and have a Morse taper in the spindle. They come with variable speed. A 3mm hole is only 1/8th. I cannot see why you would bother since I can push a 3/16th hole through one inch plate in less than a minute with a hand drill.

Randy

I've been thinking about buying a magnetic drilling machine for a while, and recently I've seen a few at affordable prices on eBay. I need one for drilling steel plates which are too big to fit in my drill press, and also for drilling frameworks which must be drilled after they've been welded together for reasons of alignment. I've seen Rotabroach cutters in sizes from 6 mm upwards, but suppose I want to drill a 3 mm hole? Can I fit a Jacobs chuck and a twist drill to a magnetic drilling machine?

Many thanks,

Chris Tidy

Thanks for the advice. It looks like there is a way to do it. Most likely I will only need two or three of the smaller sizes. The drilling machines I was looking at are made by Unibor. Any thoughts about this brand?

Wow, some hand drill! I've never been able to do that with steel plate. Actually, my main concern is not speed, but making square holes as I want to tap them afterwards. Most of the holes would be for M6 screws. The very smallest holes (3 mm) would be for pop rivets.

Chris

Drill yourself a block to line up the drill square for starters if drilling square is a concern. Center punch your locations. Spot the drill to make a large dent. Set your block and bit over the dent and drill. If you look up the speed for a 1/8th bit using HSS it is 4 times the cutting speed divided by the diameter. 4 X 100 fpm / .125 = 3200 rpm. That is the speed of a loaded air drill. Use good quality bits such a Dormer or if you really want to splurg SKF. Order stub drills with split points. If you were to cut one thousandth of an inch every revolution you would cut over three inches in a minute at 3200 rpm. I don't think you need a mag drill. If I was brave enough I would tap with a variable speed electric drill with a tap chucked. Damn I hate breaking taps off in holes though. randy

Thanks for the advice. It looks like there is a way to do it. Most likely I will only need two or three of the smaller sizes. The drilling machines I was looking at are made by Unibor. Any thoughts about this brand?

Wow, some hand drill! I've never been able to do that with steel plate. Actually, my main concern is not speed, but making square holes as I want to tap them afterwards. Most of the holes would be for M6 screws. The very smallest holes (3 mm) would be for pop rivets.

Chris

Thanks. I don't have an air drill (because I haven't got round to buying a compressor yet, but it's on my "want" list). I just have an electric pistol-grip drill, and I'm rather scared of burning it out. A guide block is a good idea, so I might try making one for small diameter drills, but I still need to drill some 12 mm and 14 mm holes in 6 mm and

10 mm plate. This would be really hard with an electric pistol-grip drill, and I have a 230 V -> 110 V transformer which could run a magnetic drill, so you can see where my thinking was going.

Will think about it some more...

Chris

For the 12 mm definitely go for a mag base. You don't need an air powered drill for those small bits... just a good quality electric at full rpm. I found labourers are brutal on small annular cutters. If you get a mag drill that cannot take a chuck then make up brazed bits like I suggested in the sizes you need. It is a lot cheaper than the cutters. A tip on electric hand drills: They expire because people abuse them. When you are done drilling a hole pull the trigger and run the drill flat out for five to ten seconds. The fan will cool the armature. If you don't then when you lay the drill down all that heat sinks into the armature windings and breaks down the insulation. This practice will significantly increase the life of your electric drill or any electric tool that has been working hard. Randy

Thanks. I don't have an air drill (because I haven't got round to buying a compressor yet, but it's on my "want" list). I just have an electric pistol-grip drill, and I'm rather scared of burning it out. A guide block is a good idea, so I might try making one for small diameter drills, but I still need to drill some 12 mm and 14 mm holes in 6 mm and

10 mm plate. This would be really hard with an electric pistol-grip drill, and I have a 230 V -> 110 V transformer which could run a magnetic drill, so you can see where my thinking was going.

Will think about it some more...

Chris

Yep! I do that, too. You can feel the heat coming off----there's no question it's a good idea.

Harold

Go to

and look at their mag drills. I have a HMD904 that is quite robust and will accept a Jacobs chuck with an adapter. I also have a smaller Hougen frame mag drill that takes Roto-Lock cutters and it will not accept a chuck.

Thanks, Steve

How did I get to my age without learning that one?

Good idea, I'll try to start doing just that.

Jeff

Again it depends on the machine. Mine has a 3/4" chuck single speed version that goes 350 rpm max. But they also make two speed versions.

Wayne Cook Shamrock, TX

Dunno! But, for me, the idea came to me when I realized that I tend to cover the vents when holding the drill motor for some things. I don't let that worry me unless I have a lot of holes to do, but I always free wheel it between holes to insure it's not over heating.

Harold