Cover plate thread size on surface grinder

I am restoring a 50/60's Janita plano grinder. The cover plates, front and sides are held on by screws. Now at the moment they are self tappers, but as the machine parts they screw into are 1/2'' think or more, I can't see these were original, unless they was a special tap for fitting self tappers ?

If I put a drill in the screw hole, drill size is 0.175''. That is a sliding fit.

I t looks to be a coarse thread, but as diameter is so small, I obviously can't use a thread gauge.

One other problem is the circular square section grinding abrasive stone has come adrift from the steel base plate, luckily still in one piece. (I still had not got round to powering up the machine which was fortunate.)

Now what is the best glue for bonding the stone back to the steel wheel ?

Would there be any advantage in drilling the steel wheel as regular intervals to aid adhesion ? At the moment it is dead smooth, not even knurled.

Mike.

I have an album of photos of the grinder on this site if anyone is interested.

Mike.

You might try a 3/16 BSW screw for starters. Assuming the machine is UK made?

Or try screwing a little plug of soft wood in there to make an impression of the threads, then measure that with a thread pitch gauge. Or a bit of plasticene etc might work tool

Edited By Hopper on 04/07/2022 12:22:26

Drive rivets would have been most likely

I very much doubt if drive rivets were used as you need to remove the cover plates to get to motor or change the belt.

I have some fiberglass filler that I can try and make an impression of the thread. I can oil or grease the thread first for easier removal.

Mike.

I recon it may be 1/4" Whitworth, the theoretical core is 0.186" but the 0.175" fitting easily is very close. If the machine is made in the USA, the thread may be 1/4" UNC which is very similar to Whitworth. Here are some thread charts from Motalia.

**LINK**

Nearest I can find so far is no. 12 UNC. core diameter is 0.170''.

Machine is British, made in Wolverhampton, but info very sparse on the net.

It cost £121.00 in the 50's, which was quite a sum then.

Stone diameter in info I found stated 10'' stone but mine is 12'', so maybe a larger model.

Top plate is around 40'' long. Be nice to get it working, I have a job lined up for it. The top plate is a massive cast iron construction and the complete machine must be 1/4 of a ton or close.

Mike.

Now what is the best glue for bonding the stone back to the steel wheel ?

I would imagine that an epoxy glue would be the thing to use. BUT you would need to do some research as to which one would be best. It would depend on the wheel size/speed/pressure generated etc.

Not a job I would fancy doing myself.

regards

The epoxy would be best for gluing the stone back on, but if it is contaminated with oil, then degreasing would be difficult.

Sparky Mike please look at your messages

Hi Mike I have used a similar grinder but with an adjustable V block on top for grinding 45 deg chamfers on hardened blocks etc. the grinding wheel had threaded inserts imbedded into the wheel structure and you screwed the wheel onto the wheel holder from underneath. you had to replace the wheel when the inserts became visible from the top. To check the thread pitch get a piece of wood turned to the diameter of the screw in hole and twist the wooden diameter into the hole and you will get a copy of the thread pitch when you unscrew it.

David

Edited By David George 1 on 09/10/2022 15:07:54