MGB & GT Forum

I've started the highly enjoyable process of drilling out spot welds for my rockers. I was told by eastwood that their spot weld cutter likes lower rpm - my dewalt hand drill has a top rpm of 2,800 rpm, while the cutter wants around 1,000.

Is this also the case for drilling into sheet metal with a regular bit? How much pressure do you apply? It's tempting to just crank the drill up, and press as hard as I can, but I think I'm burning out drill bits.

And, do you have a drill doctor? Or just buy a ton of drill bits.

I don't know if I do enough drilling to justify a drill sharpener.

Jonathan,
I bought a few drill bits from my local welding shop and they worked much better than the spot weld cutter. I think I used one bit to remove both floor pans and some of the bulkhead as well as the sills. They sell drill bits that stay sharp and work at a variety of rpm, but I prefer <2000.
Rut

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1960 Bugeye,1275, 5 speed
1970 MGB, Pale Primrose
1967 Triumph TR4a
1966 Triumph TR4a
When I went to school, they asked me what I wanted to be when I grew up. I wrote down 'happy'. They told me I didn't understand the assignment, and I told them they didn't understand life. John Lennon

I have had two drill doctor. Both were crap. The first one would always leave the trailing edge of the cutting edge higher than the leading edge so the bit would not drill a hole through anything. No matter how closely the instructions were followed the same thing always happened. The second works better but leaves a lousy finish on the bit. The procedure is very slow and adjustments are critical. Sometimes the sharpened bit will drill, sometimes it wont. Sometimes the two sides of the sharpened bit are no here near equal in size or shape.

My eyes have gotten so bad that I can no longer sharpen a bit by hand so I had to find something that would consistently work. The best thing I have found is a $30 jig sold by General tools for use with a regular bench grinder. I mounted a grinding wheel on a 1/4HP electric motor, mounter the motor on a metal base then mounted the General Drill Sharpener jig on the base. Works great. Consistent results every time and take less than 30 seconds to sharpen a drill bit.

EDIT-picture not mine but exactly the same set up



Edited 1 time(s). Last edit at 2016-08-30 09:12 AM by Gerry.

Thanks, Gerry and Rut.
Now I gotta find space to put a bench grinder...

I like that Gerry, I too have always sharpened my own drill bits and, like you are finding it more and more difficult especially with the smaller ones. I now buy the common smaller ones in packs of 10 and tend to treat them as disposable items. Expensive? yes, but trying to drill an accurately sized hole with a drill with uneven lip length is not on.
How small a drill bit can you go with that setup and still get a symmetrical grind?

As to the OPs issue, most fixed speed hand drills are for too fast for drilling steel except for very small drill bit sizes. A pedestal drill is best for bench work or a decent variable cordless will give you the best results. You have to keep the bit cool. Nothing kills a drill bits' ability to cut quicker than heat generated by excessive speed.

I have a cheap pedestal drill with 16 speeds and I tend to only use the 3 slowest no matter what size hole I'm drilling.

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• The secret to creativity is knowing how to hide your sources.
• To the intelligent person, life appears infinitely mysterious, but the stupid have an answer for everything.
First rule of forum debate:
• My opinion becomes truth if I can find one other person, on the Internet with the same opinion. It is 'chiselled in stone" if I find two!

I purchased a Drill Doctor and it was worthless. Now I use a fixture like Gerry's (Post #3) or have the bits sharpened professionally.

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Be safe out there.
Kenny

I've had a couple of the higher end Drill Doctors. The first one died (motor burned out) just as I was finishing up my car. It did good service up till then - I would have gone through a LOT of bits without it. I never had the problems that Gerry had, or if I did I didn't notice.

I hear you on the economics - buying bits vs buying a sharpener. You'll just have to estimate the # of bits you'll need, and do the math. For my car, it was easy - both sills, both floors, boot floor, both battery holders, etc..

As for speed - no faster than you need to go for the bit to cut. Start out slow and speed up as necessary. If you're running at high speed, then your bit is too dull. Heat is the enemy here, use a lubricant to cool things off - even spraying with WD-40 helps.

I found MG sheet metal pretty soft - you don't have to go fast if your bit is sharp. 1000 rpm or less.

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Documenting my project in my journal at https://www.mgexp.com/home#journal

2000 rpm is way to fast, even if you try to keep the drill bit cool with a lubricant. I use a product called 'drill chill' that works well, but there are a number products that work. I run 1000 or less with a variable speed DeWalt hand drill for big stuff and a small Delta drill press running 640 rpm for small stuff. I rarely ruin a bit, if I do I toss it and buy a new one. I pay extra for good ones with a double relief cut.

I used a 1/2 inch wide Snap-on scraper when I removed my floors. It was thick enough and hard enough and tore right through the spot welds.
First I cut out the bulk of the floor leaving just the parts that were welded in, the chipped through the welds rolling up the bad stuff as I went. I would trim of the excess when it got to be too much. Your job is different, but try lots of stuff.

The photos show some of the work and the tools I used. Once I had it out, I ground down the frame underneath to clean it up and had my bodyshop weld the new floors in. I drilled 1/8 holes in the floors, beveled them with a 1/4 inch bit every few inches in the proper spots.

Hans

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The Larry Shinoda Collection: 1965 Corvair Monza 140, 1969 L-68 427 Corvette roadster (sold), 1970 BOSS 302 Mustang. New addition 1969 MGB GT & 1968 427 El Camino!

So I re-read this and have this to add. Low speed and steady pressure, not too much, works best. It's all about physics: to much speed or pressure and friction goes up and over the limits of the bit to dissipate heat. If the metal or bit are turning blue, you need less speed, more lubricant and a new bit!

Hans

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The Larry Shinoda Collection: 1965 Corvair Monza 140, 1969 L-68 427 Corvette roadster (sold), 1970 BOSS 302 Mustang. New addition 1969 MGB GT & 1968 427 El Camino!

If your bit goes blue you've stuffed it. You'll have to grind down past that or bin it.

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• The secret to creativity is knowing how to hide your sources.
• To the intelligent person, life appears infinitely mysterious, but the stupid have an answer for everything.
First rule of forum debate:
• My opinion becomes truth if I can find one other person, on the Internet with the same opinion. It is 'chiselled in stone" if I find two!

All these pictures of rust, and I haven't had breakfast.

Gakkkk.......!

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Wayne Sanders
Rose Lodge, OR
(TD 4288)

"I don't care to belong to any club that accepts people like me"-joined Willamette Valley Club in 2011

79/65 MGB - Carmine- V-6 - T-5

This car is now very nearly completely done. Sure to find something else, but not now.........And 12 years later, I'm starting to fix things that were new when we built the car. It's pretty well de-bugged!

Something not right with the drill bit making these holes?

When doing sills, I buy 6 good 1/8" drill bits. I use them to drill pilot holes: either all the way though all layers or just a single layer if I want to keep it intact.

If I am trying to preserve the bottom layer, I only drill through the top layer with the 1?8" bit, I then follow the 1/8" with a 5/16" bit that I have been using for years. The 5/16" bit is ground to an almost flat tip that will bottom out at the bottom of the 1/8" hole.

http://i.imgur.com/2hPq5GK.jpg






If I do not need to preserve the bottom layer (most often the case) I just use a normal 5/16" bit.

Here is a link to a tutorial that I did for the Volvo community. It does a good job of detailing how to go about removing spot welds using only normal drill bits.

http://forums.swedespeed.com/showthread.php?327681-Sill-replacement-Easy-for-the-most-part

Pete

Edit:

probably should have posted this in your other thread!



Edited 1 time(s). Last edit at 2016-08-30 11:06 AM by NOHOME.

Pete and I use the same procedure for drilling out spot welds.

I have a Drill Dr and find it does a very good job of sharpening bits.

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Canadian Modern MG Rover Car Club - www.cmmgrcc.com

MOWOG Garage serving the needs of all Post Abingdon MG owners in Lambton Co. since 2011.

I've used all kinds of spot weld cutters, and generally settled on using a 5/16 bit. But I also have been really impressed with the Harbor Freight spot weld cutter. http://www.harborfreight.com/3-8-eighth-inch-double-sided-rotary-spot-weld-cutter-95343.html

I've used one for almost all of the spot welds on my Chevelle project, and it's not worn out at all. Need to center punch each spot weld or it walks all over the place, but once it starts cutting it's fast.

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Ryan

Pete,
You taught me well...I still do the same!
Rut

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1960 Bugeye,1275, 5 speed
1970 MGB, Pale Primrose
1967 Triumph TR4a
1966 Triumph TR4a
When I went to school, they asked me what I wanted to be when I grew up. I wrote down 'happy'. They told me I didn't understand the assignment, and I told them they didn't understand life. John Lennon