Fixing metal dowels

I think I obtained a kit for G. Thomas'' scribing block under the impression that the 2 x A3 pages would have any details required for a well-read novice; but that proved a little optomistic. Part of the construction involves the (permanent) coupling of two machined pieces (presumably precluding soldering). The plans indicate 2 dowels of fine silver steel, but with no detail on fixing. Would it be simply a loctite job?

Thanks in anticipation. Bill

Idealy dowels secure two parts of a job together by means of a reamed hole, which is produced with the two halves clamped together and drilled and reamed at one setting. This allows the two halves to be seperated if needs be, unlike loctite! If you don't have a suitable reamer you might get away with double drilling, using a factory ground drill to produce the size hole.

Experienced toolmakers used to have worn reamers set aside exclusively for dowel holes . Together with proper hardened dowels,( which are slightly oversize from nominal size), these gave a nice light drive fit wthout any loctite. If parts are to be separated from time to time it's advisable to add knock out holes or use tapped dowels to facilitate easy removal. Blind dowel holes sometimes had side air holes added so that the dowels could be driven in all the way without the air pressure trying to force them back out. Or alternatively a small air relief flat could be ground on the side of the dowel. I've seen side air holes used with close fitting punches to hydraulically drive dowels out . Even seen match heads used to fill up side holes and then struck with close fiiting punch to drive dowels out.

Cheap H7 Tolerance reamers will not give the required fit for tight dowels without using loctite. Unfortunately H6 reamers are a little more expensive. Most old time toolmakers would cringe at using loctite on dowels as the main purpose of using dowels was to locate parts without any clearances in the dowel holes and parts could be separated and put back together in exactly the same position. If the dowel hole is slightly oversize it can be closed up to provide a tight hole by placing a hardened ball over the hole and given a good rap with a hammer. Don't overdo this as it can move the hole in soft metal. We never let the toolroom foreman see us doing this as it was considered bad practice ( bodge up) ! 

Hi Dino,

 

You brought back a lot of memories for me of my old toolroom foreman and his insistence on close fitting dowels. On some press tools we would drill a small hole (1/32" or so) through the tool from the dowel so that it could be driven out with ground up match heads. Not silly safety matches mind you, but real red ones that could be literally 'struck' with a hammer! Boom! Good old times. No loctite then, Mind you there was also the boring alternative of the smaller dowel driven from the rear into a grease packed hole - that was nowhere near as satisfying .

 

Thanks and best regards,

 

Terry

Very well chaps, I'll give the classical tight fit option a spin and see if it works in this application. I can always revert to the dreaded Loctite if needs must.

Thanks for the lesson; you now have only yourselves to blame for what will probably be an unending trickle of mundane inquiries from me.

Cheers,

 

Bill

Hi ! Terry,

Some toolmakers used Bees' Wax instead of grease as a hydraulic medium . Certainly smelled a lot sweeter !

Proper hardened dowels have ends that are shaped differently . One end would have a slight chamfer to guide the dowel into the hole. The other end would have a radius form so that when struck with hammer or punch, the end would not mushroom or be damaged.

Hi Neil.

 

I remember those dowel ends well, we used bought in ones. Sometimes my toolmakers used tallow instead of grease, (Yuk!!) it was freely available because the electricians used it as a lubricant when cutting threads on conduit tubing and it would liquefy easily under the heat generated when compressed with a hammered dowel. I can remember the smell still.

 

Best regards

 

Terry

Posted by KWIL on 25/01/2011 16:55:18:
In the construction notes for GHT Scribing Block as set out in the GHT Model Engineer's Workshop Manual (page 24), these two holes are drilled 1/16" and the MS pins dropped in and the two blocks are SILVER SOLDERED.

Edited By KWIL on 25/01/2011 16:56:30

Aha; that's interesting. If I get brave enough' I might give that a crack. Thanks for the (ultimate) reference material, much appreciated.

Bill

Posted by Terryd on 25/01/2011 22:32:43:

Posted by William Rule on 25/01/2011 23:26:55:

yes, isn't it wierd that what you did with the keys 5 minutes ago is a complete blank, but some smell from eons back still remain as sharp as they ever were.

Hi William,

 

Yes, it's nearly 50 years from that time, but I can still see and smell that block of off white tallow as if it were yesterday.

 

Best regards

 

Terry

 

PS

I still get the occasional whiff of carbolic soap and hot water to remind me of Junior school occasionally!!   Mind you, surely that was only yesterday? 

 

T 

TerryD - The smell of hot Russian tallow From the 'Bodies in the white' leading up shop over at Press Steel. They stopped using it when the stopped making the Royce/Bentley body shells. It was nearly as rancid as the smell of the oil in No3 canteen opposite my office. Oh my God, 'Holy Joe' the head 'Hash Slingers Mate (3rd Class)' who ran the place did not change the stuff from one years end to the other. Mixed with the smell of 'One Armed' Fred striking Swan Vesta between his thumb and forefinger to light his Condor Flake of if he could get me to cut it for him some Condor Plug. Towards the end of the week it would be the 'Black Twist' 'baccy and that was rank!.

One of the smells I remember from when I was a kid is hot aluminium, Dad had a Jowet Bradford, and it had a desinctive smell, more so in wet weather. I was reminded of it two or three years ago when I came across a Bradford at a vintage car gathering. We travelled a long way in that vehicle, vertually from one end of NZ to the other. Ian S C