''D'' bits

[lancelot]

Hello all,
whilst roaming about the local flea market, I managed to collar an almost complete set of ''D'' bits in 1/32 increments, they all looked as if unused except the 9/32 where the shaft had been scored., they were well made and appeared to have been hardened and ground to finished size.
I have as yet , not gleaned a lot of information on the use of these tools, other than on how to make one, so would someone with the ''knowledge'' kindly instruct me in their correct use, i/e ...setting up to drill on centre of a marked hole position e/t/c...I would appreciate any help or advice on this subject,
All the best for now,
John.

[gwrfan]

Hi John,

The only main use of D-bits that I know of is for squaring up, or flattening the bottom of a drilled hole. I'm not sure that you should actually use the bits to drill a hole, although I have sometimes used them to slightly enlarge a drilled hole, similar to a reamer.

Hopefully others can provide more info, which might even be useful to me, haha.

Regards from Cornwall

Geoff

[alanstepney]

I often use them instead of a reamer. Useful if you want a true hole and dont have a reamer of the correct size as D bits are quick and simple to make. (Also, cheap!!)

They are a single point cutting tool so speed needs to be low. Look up the speed for CARBON not high speed, drill of the same size, half that, and then reduce that slightly.

Feed should be continuous, so that it is cutting not rubbing.
Cutting depth of the order of a thou or three, depending upon size.

Keep them sharp, on an oilstone, or even better, one of the fine diamond files.

They will also centre a hole that is not quite true, but only within limits. Might need several cuts with slightly increasing size D bits to correct any appreciable error.

Oh, yes, they are ideal for bottoming blind holes.

[gwrfan]

Thanks Alan,

I actually looked at your 'page', but didn't spot anything there, haha. Useful info, thanks again.

Geoff

[lancelot]

Is it not a blinking nuisance having something you know what it is and what it is for but not what to do with it !!!?, I must be getting old,,, but I digress, this is just exactly the kind of information that I was looking for, never having used this type of drill reamer before, thank you all for the most useful tips, and all the best for now,
John.

[alanstepney]

I should have added, it is essential to keep withdrawing them at VERY frequent intervals.
Unlike a twist drill, there is nowhere for cuttings to go and so given the slightest chance they will score the bore and possible jam the whole thing solid. Not what one wants !!

When I make them, I usually reduce the diameter from about 1/8" to 1/4" (depending on diameter) away from the cuttibg edge, by a thou or two. Just enough to ensure that the main part doesnt rub, which causes friction, which, particularly on brass, will cause it to jam.

Whilst silver steel is the best material, for brass and other softer metals, I frequently use ordinary mild steel. Case hardened if it is for several cuts, but even in the natural state, it will cut OK and do a whole or two.

[the_viffer]

alanstepney said:

I frequently use ordinary mild steel. Case hardened if it is for several cuts, but even in the natural state, it will cut OK and do a whole or two.

Is that a whole hole?

[gwrfan]

viffer said:

Is that a whole hole?

So do two whole holes make a hole hole? ;D

[alanstepney]

Errrum, that was todays deliberate (??) mistake.

[the_viffer]

alanstepney said:

Errrum, that was todays deliberate (??) mistake.

Let him who is holy without error cast the first stone

[Phil Sutton]

Ah,but would that make him more holey than righteous?

Phil

[the_viffer]

philsutton said:

Ah,but would that make him more holey than righteous?

Phil

But surely we would not D-bit the goodwill we holed in him?

[Tel]

This thread is beginning to bear an eerie resemblance to my socks

[the_viffer]

tel said:

This thread is beginning to bear an eerie resemblance to my socks

You're right. It stinks.

[Phil Sutton]

In fact it's getting a bit cheesy.

Phil

[gwrfan]

Hi All,

Returning to the subject of D-Bits, I was this evening thumbing through some 55-year old copies of the Model Engineer (as you do), and found two very useful articles on Making and using D-Bits:

Vol 103 No 2584 Nov 30th, 1950 - Making D-Bits
Vol 103 No 2585 Dec 7th, 1950 - How to use D-Bits

If anyone is interested in the articles I can copy them, and email attachments. The articles are very informative.

Geoff ;D

[lancelot]

Hello Geoff,
would be most appreciative of that, if you could do it for me.
All the best for now,
John.
ps... please place GWRFAN in subject matter.

[spurley]

Yes please copy me on the email.

Cheers

Brian

[gwrfan]

Hi John and Brian,

OK, I'll scan the pages later tonight or over the weekend, as I work Fridays and Saturdays. I should have added that although the articles are years old, they appear to be still up-to-date, and interesting reading.

Geoff in GWR Land

[steamjohn248]

I would also appreciate a copy of the 'D' bit article on the E mail

cheers

steamjohn 248