The Stovebolt Site Forums The Parking Lot Big Bolts Brake Drum Micrometer?

This isn't actually Big Bolt related, although I could use it on Big Bolts by using different lengths on what I am making. I got this posted on another board concerning a Brake Drum Micrometer for 11 inch Drums. I want to post it here as I know we have some pretty knowledge-able people on here. Here is what I posted:

I've been in the market for a Brake Drum Micrometer. I like the Ammco 8500's but they are pretty expensive new and used ones aren't real cheap either. Then a lot of used ones need to be Re-calibrated and that tool is about another $100.

I've decided to try to make my own out of a Dial Indicator that I bought. I'm going put an extension on it to equal the inside measurement of an 11 inch Brake Drum.

My question is, is the inside measurement of a brand new drum Exactly 11 inches?

I'm planning on having it set to about zero on a brand new drum, and I should therefore get a pretty accurate reading on a used drum.

I'm going to try to make it as accurate as I can.

Any input would be appreciated.

Thanks

Bill

I'm not the guy to be answering this but my experience delivering parts makes me wonder about some of the overseas stuff. First off one of the better shops her TURNS all new rotors and drums. I've watched and you'd be surprised to know they all are not "true". I have noticed another shop starting to do this as well. I suspect they are having problems with some new rotors/drums.

So, if being within a few thousandths of an inch is OK then I think you can do it.
I'm interested in what the "pro's" say to.

Hy C10 - C90 Bill, my experience is more with truck/bus drums, but I have seen them typically .010" -.020" undersize when new, I believe this was done so we could cut any mounting distortion out of of the drum, and still be at size or slightly under size. This may be the case with smaller drums as well, hope that helps.

I got the same report. That is actually another reason why I am going ahead with this project. I have many USA made old Brake Drums that I want to check.

One guy actually told me that the lug nuts bolt holes were not on center on some of those overseas ones.

Bill

3B, I was hoping that you would drop by.

Edit: I just re-read what you wrote and now see that if I made it at 11 inches, and it is under sized, it will not fit. I'm wondering how the Professional Made Micrometers are set?

Maybe I could set up the Indicator to show both ways? Undersized or Over.


Bill

There's one on Ebay right now for 80 bucks. Better buy it quick! Search "Brake Drum Micrometer".
Jerry

Jerry,

Appreciate the info. I check Ebay now and then and seem to lose out on the cheaper ones, but also as mentioned above, a lot of used ones need to be Re-Calibrated. The Re-Calibration Tool alone is about $100. Seems like minimum investment would be about $200, with the shipping and all. They also sell a Rebuild Kit, which is about another $35 or $40.

If my idea works, my investment will be about $15.

Bill

Bullshorts! Buy it, send it to me, and I'll calibrate it. I've got micrometers all the way up to 12". If you don't want it, I'm going to buy it.
Jerry

C10 - C90 Bill, on the subject of tools I'm continually amazed at how hobbyists go overboard and buy way more tool than they need. This recently came up with regard to double flaring tools also when perfectly servicable units inexpensively available on ebay were rejected in favor of industrial stuff suitable for a production facility.

In 1965 when I was a 20 year old college kid who had just bought a '36 Chevy pickup project, I wanted a tool to check brake drum sizes. One of the machinists in the geology-chemistry building at UCLA made me a 5/16" diameter rod with ball ends exactly 11" long. I've been using it to check brake drum diameters since then, using that rod and a set of number drills to measure the drum diameters.

I still have the '36 pickup and the 11" rod.

Ray, email [email protected]

I have an Ammco 8500H at the shop. Years ago I made a 16 1/2" standard to check our drums. A 2 mm bit is used for a go or no go and that gets us pretty close to the .080 allowable oversize to reused. I'm not sure I have anyone working for me that can read the mike anyway. We chuck up new drums on a lathe and check for runout and occasionally have to cut a new Gunite made in USA drum.

Appreciate the additional info y'all.

I like the Rod and Drill Bit idea.

The Dial Indicator I have has a "Set Arrow" therefore I believe I will be able to make it work for Over and Under. Just need to do some accurate measuring.

Bill