Re-fit a Stanley 80 scraper with new blade-strap thumbscrews

[Gene Davis]

I got an old one at an eBay auction, everthing OK about it, except that a previous owner lost one of the thumbscrews that secure the blade-strap to the body, and replaced it with an old brass screw and a square nut, oversized, for a washer. I cannot tell the age or country-of-origin on mine, but it has the concave edge on the trailing edge of the sole.


These old scrapers, perhaps British-made, had paddle-style thumbscrews with a funky non-ASTM thread. The newer ones that Stanley is selling today have knurled slot-head shouldered thumbscrews that have a "standard" 1/4-28 thread.

To drill out and retap is pretty easy, I think. A #1 bit at 0.228 diameter, then the 1/4-28 tap, is all that is needed. The 0.228 bit will take out the threads plus more in the threaded holes for the smaller British-sized screws.


Stanley sells the parts kit, two thumbscrews plus a new strap, and I've ordered it. Won't do the re-fit until parts are here and examined carefully.


Anybody else done this?

[Matthew N. Masail]

I haven't done it with old tools, but I can't see where you can go wrong and long as your careful about the drilling+tapping angle. most likely it will be better than ever.

[Bill Rittner]

I just tapped a 1/4-28 thread in steel yesterday. The proper tap drill is #3.

[Gene Davis]

That might be right, but the chart I have shows doing a #3 for softer materials like aluminum, brass, and plastic, in which one wants deeper thread engagement. My chart shows a #1 for steel and iron. I'll maybe take a piece of steel and drill with a #3, then a 7/32", and finally a #3, then tap all with the 1/4-28, and try the screws in all. Perhaps I'll like the fit in the middle, the one bored first with the imperial-sized drill.

[Jonathan McCullough]

Yes I did this for a scraper I found. The previous caretaker had put an 8-24 (from memory) screw in because s/he couldn't find the proper screw. Here's how I did it. First, find the largest twist drill that will fit in the hole. Put that drill in your drill press chuck. Then lower the quill so that the bit goes into the hole in the scraper. Then clamp the scraper in your drill press vise. This could be a little awkward and may require some creative shimming in the vise since the angles on the scraper don't lend themselves to clamping.

Once you've got everything set, this procedure ensures that the new hole you drill will be concentric with the old hole and the work is secure. You can put the final twist drill in the chuck that matches the tap you'll be using. I just got a thumb screw and matched the drill and tap set to that. Drill the hole, take the twist drill out of the chuck, then put the tap in the chuck. Don't turn the drill back on obviously, but use the feed to start the tapping, since the chuck and tap will still be concentric with its corresponding hole. I used some oil with the tap and went slowly, backing up frequently to clear the chips and everything worked out fine. Thumb screw went in first time and had it back to work pronto.

[Bill Rittner]

The #3 tap drill for a 1/4-28 thread comes from all the charts I have in the machine shop. These tap drill charts are based on 75% of full thread which has been industry standard in the machine trades since I came into it. The material to be threaded has nothing to do with it, it is the % of full thread you want that determines the tap drill size. A #1 drill is 0.015" bigger than a #3. With a #1 tap drill you only have a thread profile that is 0.011" deep. That has to be less than 60% thread. This would be weak. Using the #3 as specified in all the industrial charts yields a thread profile that is 0.0185" deep. this would be a much stronger thread.

Also, I don't recommend using multiple drills to get to size. Drill your holes to size. A drill is made to take a bite on it's cutting edge. That is what centers it and keeps it going straight.

This is just my opinion based on accepted machine shop practice. It is your project so you have to do it your way.