Drilling brass – seizing

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

A ball ended end mill is better than a simple square ended mill for two reasons :

 

(1) The bore is truer for roundness and diameter . This is because there is a natural

stabilising action arising from the cutter/hole geometry .

 

(2) The finish in the bore is better – very nearly as good as a reamed hole .

This is because the cutter basically has no corners and the cutting action is

smooth and progressive .

 

 

[mgjParticipant @mgj]

Sorry – to be sure – I wasn’t suggesting using an endmill in rotation. Specifically Andrew said he had no boring bar of a size. So when I want a little boring bar and I don’t have one to size, I just take an endmill, mount it in the tool post and use one tooth as a boring bar.

 

Endmill isn’t turning – its just the unwitting supplier of a tooth. You have to offset the toolpost a touch to give a whisker of clearance.

 

This will probalby work in Andrews case because the job is a bearing shell, so the hole will be fairly short. Unless one has a long series endmill of a size and hte job warrants such a length.

[Anonymous]

First a few comments. I do have small boring bars, but it’s a whole load quicker to drill out material rather than use a small boring bar. Second, the bearings are a bit over 2″ thick, so I suspect my small boring bar, at 8mm diameter, would have chattered more than a Hampstead resident.

 

Terry: I did consider a D bit, but I’d have to make it, and I’m impatient!

 

In the end I found a slot drill in my tool store with relatively short flutes but a long shank, and where the flutes are larger than the shank. Put it in the drill chuck in the tailstock and it went through easy-peasy. I then bored to size using a 20mm boring bar. Just as well I checked the drawings first as the bore is 1.125″, not the 1.25″ I originally quoted. Here’s a picture of the set up, with the bore finished:

 

The slot drill used is sitting at the front on the cross slide, and the ground to size gauge used to measure the hole is perched vertically on the toolpost.

I can’t believe how easily it all went, after the travails of last night. Thanks to all those who made helpful suggestions, and especially to David, Michael and mgj for the slot drill discussion.

 

Tomorrow evening I’ll try the next one from scratch using what I’ve learnt!

Regards,

Andrew

Edited By Andrew Johnston on 30/01/2012 21:08:37

[TerrydParticipant @terryd72465]

Posted by Andrew Johnston on 30/01/2012 21:06:38:Terry: I did consider a D bit, but

 

…………….I’d have to make it, and I’m impatient!…………………………..

Andrew

Edited By Andrew Johnston on 30/01/2012 21:08:37

Oh Andrew,

 

The last ‘D’ bit I made (and I’ve made a few) took about 20 minutes from initial selection of material to tempering and using, about the amount of time it takes to make a few comments on this forum. Much less time than searching a catalogue and ordering an expensive substitute.

 

Best regards

 

Terry

[Ken JohnstonParticipant @kenjohnston10955]

Thank you one and all for your advice. Sorry I have not come back in before now. Redecorating and grandchild.
The hex bar I used was found in a yard years ago so no idea what it is. It does come off in small chips and screams as it goes, and to me, dos’nt seem as dark ? coppery as bronze or gunmetal. Mind you, I’ve not much experience of them. I had a couple of hours yesterday (emulsion drying), went out, rather chilly, and cut an inch or so off one of the jamming drills. Resharpened + neg. rake, not as bad this time but still jamming. I had thought of relieving the drill sides a few mm below the facets just to try it.
I then, ala asymmetric sharpening, used a forcing bar, idea from Mr. Sparey’s book, well a piece of wood between the toolpost and the drill shank to push over the drill a touch to clear the existing hole out. That worked. I then picked a 9/16 drill, touched the edges and tried again. After a lot of “pecking” running the coolant over the outside of the job, WD in the bore and drill pulling out a couple of times I got thro. I can now use a boring bar.
I remember I was drilling out a brass electrical cable gland on a pillar drill, might even have been for the QE2, bit above inch, when the drill jammed, whirled the machine vice complete with gland round until it hit the drill pillar. The vice of course was not fixed to the table.
Promptly snapped the drill . Luckily for me the machine was at the rear wall of the shop so nobody really noticed the bangs amid the general noise. Bits into scrap bin and try again. I’ve been a bit wary of brass since.

Mike Williams. No. The piece protrudes beyond the chuck and wall is still about 6mm. I think a D-bit might be the answer. But no silver steel.

Jason Udall. Funnily I did think it seemed to work harden.
MGJ. I will try a test with no pilot with my old drills. High feed rate. Fear is the answer.

Ian Hewson. I’ll try a brand new one. My old drills could, are, 10’s of years old.

 

Andrew Johnston. Did not know my son did model engineering.

 

Regards to all.

[mgjParticipant @mgj]

I think all modern drills are ground with back taper, so they should clear. I always bang heaps of coolant on to limit expansion – nothing special, just the ordianry 20:1 mix of cutting oil and water, but lots of it.

 

Like you fear caused me a lot of grief – I approached gently and all that stuff. And its exactly what one shouldn’t do, because a soft approach allows the drill to catch and then drag the holder forwards into the backlash. Once I kind of understood hte logic, stopped drilling pilots and deep centres, and banged the drill in firmly to get the holder pushed back agin that feed nut, and hard ernough to keep it there all my drilling in bronze problems went.

 

(You won’t achieve a high feed rate – what you will achieve is a an end load controlling the drills advance)

 

I don’t claim its the best, or even the only answer, but its done me OK both drilling tough materials, and parting for a while now.

[Sub MandrelParticipant @submandrel]

I had a really good idea yesterday that would help with spinning drill vices.

 

I will try and find time to make a prototype.

 

Neil

[Anonymous]

Oh Terry,

 

No way I could make a D bit in 20 minutes; I’d still be setting up the machine vice and installing an appropriate cutter. In fact I seem to be slow compared to everyone else on this site.

 

Anyway, moving swiftly on, I’ve finished the gunmetal bearings:

 

Thanks everyone for your help.

 

Ken: Even odder, I don’t remember my father being called Ken! It was unfortunate that while I was studying for my Ph.D there was another reseach student in the department with the same name. At least I was working in pulse compression radar and he was into nuclear engineering.

 

Regards,

 

Andrew

[VersabossParticipant @versaboss]

Posted by Ken Johnston on 31/01/2012 15:04:57:
Thank you one and all for your advice. Sorry I have not come back in before now. Redecorating and grandchild.
The hex bar I used was found in a yard years ago so no idea what it is. It does come off in small chips and screams as it goes, and to me, dos’nt seem as dark ? coppery as bronze or gunmetal.

[end quote] – cannot go back to the normal entry position in this d*”% editor.

Anyway – small chips, screaming, work hardening and a yellow colour almost like ordinary brass – I would bet that this is aluminium bronze then.

(I liked the line “redecorating and grandchild” – hope you did not the firstr to the second )

Greetings, Hansrudolf

[GoCreateParticipant @gocreate]

Hi

If you sharpen the drill with one flute slightly longer than the other the drill will cut slightly over size.

Not good practice but maybe will prevent jamming?

 

Just a thought.

 

Nigel

[Ian S CParticipant @iansc]

Nigel, Michael Williams suggested that on the 29th Jan, so you are not alone. ian S C

[DMBParticipant @dmb]

Hi Andrew Johnston,

Looking @ the piccy in your posting 1st Feb @ 22.42, the 2 big castings both appear alike but if as I think, they are Traction Engine shaft bearings, shouldn`t they be handed?

Have looked back thro` all prev. posts on this thread and cannot see any mention of their use, so what are they for?

Regards,

John.

[Anonymous]

Hi John,

 

In my first post I mentioned ‘traction engines’; so you are correct that they are the crankshaft bearings for a traction engine. But also note the plural; I’m building two identical engines. In the picture there are two sets of bearings; each engine uses one large and one small casting. The small (round) castings go on the outside of the lefthand hornplate. The large (rectangular) castings go on the inside of the righthand hornplate. And if I’ really lucky the bearings will line up!

 

Regards,

 

Andrew

 

In this thread:

 

http://www.model-engineer.co.uk/forums/postings.asp?th=37921&p=4

 

I’ve posted a picture of the hornplate assembly, which may clarify the arrangement.

[Author]

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