Centre drills

[spurley]

Hi All

I have now reached a point in the construction of my 3.5" gauge Tich where LBSC calls for the use of a 'Size E' centre drill. I have BS sized centre drills and a fair collection of various workshop practice/engineering data books but cannot find a correlation in any of them. I have also tried google/yahoo/askjeeves searches to no avail. I tried Slocumb drills also thinking they might be the same.

Any help gratefully received, please.

Cheers

Brian

[GeorgeRay]

Brian
I dont think it matters exactly what size it is so long as the diameter is well less than the number 40 drill that you have to drill with. I would guess that it equates to an 1/8th centre drill which providing you dont go right down to full diameter would seem to work. None of my reference books give centre drill sizes other than in imperial units.

[spurley]

Hi George

The part of the construction is I've reached is regarding pipe unions, LBSC specifies the use of a size E centre drill but I'm not quite sure what the actual size is. I can carry on with the work but would just like that little detail clarified if possible!

Just as an aside; is there a recommended relationship between pipe OD and suggested hex for the union nuts? I am presently working with 3/32" pipe and 1/4" thread so I'm using 5/16" hex. This seems to look OK but again I wondered if there is an easy 'look up' chart for union nuts?

Cheers

Brian

[baggo]

Hi Brian,

Your query intrigued me as I had not heard of 'letter size' centre drills. After wading through my ME index I eventually found the info in an artcle by "Duplex" in Volume 98 number 2448. This suggests that the letter sizes were American. The sizes given are:

Size........Dia. of Pilot.........Dia. of Body

A................3/64"...................1/8"
C................1/16"................13/64"
D................5/64"................15/64"
E................3/32"..................3/10"
F.1.............5/32"..................7/16"
F.2.............3/16"..................7/16"

Re. pipe unions - 3/16"x40 is usually used for 1/16" and 3/32" dia. pipe, 1/4"x40 for 1/8" and 5/32" dia. pipe, 5/16"x32 for 3/16" dia. pipe, and 3/8"x32 for 1/4" pipe.

Hope that helps,

John

[Tel]

spurley said:

Hi George


Just as an aside; is there a recommended relationship between pipe OD and suggested hex for the union nuts? I am presently working with 3/32" pipe and 1/4" thread so I'm using 5/16" hex. This seems to look OK but again I wondered if there is an easy 'look up' chart for union nuts?

Cheers

Brian

for 3/32" pipe I use 5/32" thread and 7/32" hex material.

Similarly
1/8 Pipe 1/4" thread 5/16" hex
3/16" pipe 5/16" thread, 3/8" hex
1/4" pipe 3/8" thread 1/2" hex and so on.

As another aside, when I am making union nuts I make 'em 'square' - that is -

3/8" hex 3/8" long. 5/16" thread 5/16" deep
5/16" hex 5/16" long. 1/4" thread 1/4" deep.

If you use this system you don't have to remember anything at all
;D ;D ;D

[spurley]

Hi guys

Thanks for the advice.

I am glad I wasn't the only one baffled by the letter size centre drill. I expected the info to be easier to find and can't imagine why LBSC would specify an American sized drill But there it is!

I'm off now to connect up my lubricator and finish off a few more details before starting on the boiler.

Cheers

Brian

[GeorgeRay]

Brian
I should be very careful about using the American size E centre drill, coz it obviously isn't the size meant by LBSC. In his instructions for the lubricator check valve the instructions go 'Chuck a bit of 1/4 round rod, face and centre deeply with size E centre drill. Drill down about 7/16deep with 3/32 or no 42 drill.'
This wouldn't fit in with the american size E where the pilot is 3/32. I suspect that the British letter sizes ran the other way round and size E was a small if not the smallest size.

[spurley]

The plot, if not the drill size, thickens

Anyone have a definite solution to this please?

Making unions doesn't seem to be too hard, ask Arthur Scargill!!, but I would like to know what LBSC meant.

Cheers

Brian

[baggo]

George may well be correct when he says that 'our' system may have been different to the American. I've looked back through the Tich articles and when machining the wheel castings LBSC sugests using an A or B size centre drill when drilling the axle holes. One would assume that a larger diameter centre drill would be used for this operation.

John

[spurley]

Hi John

I am at the last few stages of chassis construction just before boiler making commences; my chassis now runs on air!

I've been fairly religiously following the Tich construction book, Simple Locomotive Construction by LBSC (presumably a transcript of the ME articles you are referring to?), and have, on rare occasions, updated the method or material he specifies. I have made some unions and nuts but I am still baffled by his reference to letter sized centre drills.

I have sets of Workshop Practices books from Caxton, Newnes etc dating from the fifties up to fairly recent but none of these gives any other dimensions than the BS series of centre drills.

Cheers

Brian

Still wondering what's going on!!

[standardsteam]

Sorry to go off-topic, but I'm building a Tich also (or finishing one that my dad started not long after LBSC described it!) and silver steel is stated for the guide bars. I'm coming to the conclusion I'll have to substitute (stainless) or mill out the required size, unless anyone can point me to a supply in those dimensions?

[baggo]

You could use ground flat gaugeplate for the slidebars which is available in many sizes. I've bought it from RS Components in the past but you could try Sheffield Gauge Plate Ltd:

www.ground-flat-stock.co.uk/

Their prices are cheaper but there may be a minimum order. Their nearest size is 1/8"x3/8" so you would have to mill it down.

Most Model Engineering suppliers stock gauge plate but the sizes tend to be limited. I made the slidebars for my Flying Scotsman from strips cut from 2" wide stock. It's pretty hard wearing even if not hardened (it's actually tool steel!). It's good stuff for making valve gear parts as well.

John

PS just noticed that Sheffield Gauge Plate Ltd charge £12-50 postage for orders less than £150! Folkestone Engineering supplies would be a cheaper option I think.

[Tim Bayliss]

A thought on centre drills. Most people (including myself) use centre drills to provide a start hole for a twist drill in the lathe but this is not their main purpose. They are really for providing a hole to run the lathe centre in. Could LBSC have meant a letter 'E' SPOTTING DRILL, which is actually the correct type to provide a start for a twist drill??
Tim

[baggo]

Hi Brian,

I wouldn't worry too much about those letter sizes as you obviously can't get them anymore! Like you I,ve checked all the sources I can and the article in ME is the only reference I can find.

In his earlier articles LBSC never mentioned any specific sizes, just " centre with a slocombe". It is possible he brought a set back with him from the USA when he returned to England or one of his American friends sent him a set. The letter E size crops up a lot in later articles, especially with reference to pipe unions. I think the idea was that the centre drill is used to make the conical seating for the pipe cone so the diameter of the centre drill body should be at least as big as the diameter of the union (eg 1/4" dia. for 1/4"x40 union). The diameter of the pilot should obviously be no bigger than the diameter of the central hole.

Glad you've got the Tich chassis running on air. It's a nice feeling to see all that hard work come to fruition!

John

[spurley]

Hi John

Yes I think I will have to move on! I will ask LBSC when we meet in 'that shed in the sky'

To Standardsteam, I used 1/8" gauge steel (bought for making the expansion links as well) and cut off a piece 3/16" wide for my slide bars. I bought mine from Macc Modeleng Supplies, cost £8.50 for 18", but they seem to be a little frustrating at present.
I would also recommend, if you haven't already passed this stage, making a spare piece specifically as a punch to clear out the crosshead 'hole'. I made my crossheads up and during soldering had the problem of the spelter working inside the crosshead hole, I cleared it with a combination of a piece of surplus guide bar and careful filing. Even with this I finished up with slop; this was cured with very carefully applied shim stock. So far so good. If you think I can be of any help with your Tich, please don't hesitate to contact me.

Cheers

Brian

With his BS centre drills ;D

[lancelot]

Hello Brian,
Baggo would appear to be right in his assumption that it was an American product, ie. centre drill, I have spoken to a few tooling manufacturers, and they all agree that no letter designated ''centre drills'' were produced in this country, ie. UK.
This is the closest I can find to what he...LBSC... may be talking about.

E1 HS... combined drill countersink...size...E1...body...19/64''...drill....089''

Information taken from this site...

www.victornet.com/cgi-bin.victor/productlist.html

All the best for now,
John.

[Uzzy]

I contacted Tracey Tools to see if they could help see thier reply below.

well it's the same as BS3 Cen drill , 1/4 " body.hope this helps?

[Tim Bayliss]

Is it a coincidence that a letter 'E' size drill is also 1/4" (6.35mm) dia?
Tim

[standardsteam]

Thanks for the replies re:slide bars, I skipped past the motion and completed the boiler. I bought some gauge plate a while back with the expansion links in mind.

For me I pick a centre drill out of the pile which is smaller than the hole I intend to drill, or is big enough to cut the cone for the union to fit in! After I've turned and threaded the outside I know just about where to stop feeding the centre in!

However, I'm a bodger in the workshop, so any advice I give must be treated with caution!

[Tel]

You're not alone Mr Steam (or can I call you Standard?) I do it that way as well