Identification of D-bits

Evening all,

The two D-bits I have attached to this post have been in my junk box for a long time.

One is 0.136" dia. the other 0.179" dia. I guess they are HSS.

Both about 3-4" long.

Can anybody suggest to me what branch of engineering they were used in.

They are not home made and I can't read the coding on the larger one apart from the number "18", the smaller one had no writing on it at all.

Len. P.

D-bits used to be used in gunmaking, as I understand it, but I think they often were waisted between the cutting end and the shank.

Neil

They look like half round drills, used for drilling holes in brass. See for instance:

http://www.drill-service.co.uk/Product.asp?Parent=020320040000&Tool=388

Regards,

Andrew

They might have been used to make nice clean holes for the rivets and roves in clinker boat building.

Splitting wood on a plank is a disaster and these would make clean holes.

Clive

What are "roves" Clive?

Len.

'Surely' the 18 is the size unless 179 is actually written on it..

It is probably not coincidental that they are tapping size for 3BA and 1BA respectively.

A regular jobbing D bit would not be made so long and fragile. Therefore probably a more controlled environment such as production machinery and being used only to size a predrilled hole for tapping. 3BA is common in electrical fittings.

A couple of innaccuracies have crept in there in my info.

The 4" long drill x 0.136" dia. has the following code just discernible on the shank in this vertical format.

29

HS

US

The 3 1/4" long drill x 0.1695" dia. has this code on the shank:

18

HS

US

I had to put them under a high power magnifier to read the info on the shanks.

Len.

Hello Len, Roves are used with copper rivets when building clinker type boats and you drill through and put the rivet in and a 'Rove' like a domed copper washer is put over the rivet and the excess is clipped off and the rivet then peened over the rove.

Makes a nice water tight joint, also used to keep the rib work tight against the inside planking.

Clive

Hi all,

Many years ago I was employed as a tool & cutter grinder in the meter shop at

Ferranti's, Hollinwood, Oldham. One of my many jobs was to produce D-bits, they

was normally made from ground HSS drill blanks supplied by Dormer and made on

a Cincinnati No 2 cutter grinder. The finished D-bits was then used on small lathes

to ream holes in brass gearwheel blanks, the reamed blanks would then mounted

on a mandrel to have the teeth hobed on a Micron gear cutter.

Years later all the brass gears was superceded by precision moulded plastic gears.

Bert Ashton.

Edited By BERT ASHTON on 15/03/2012 14:54:13

As Andrew has pointed out they are half round drills. They are number drills size 18 and 29 hence the marking. HS would mean HSS steel and US should be obvious.

Russell

I think the responses so far have more than answered my initial question.

It would be interesting to know though what components warranted using a no. 29 d-bit 4" long!

I failed to spot the connection with number drills, thanks Russell.

Thanks for your help lads.

Len. P.