Milling internal rectangles?

[Cornish JackParticipant @cornishjack]

G'day all.

Latest swarf making exercise is a Tiny Power Vertical Twin. Among the various bits still to do are the steam chests/valves. These appear to require internal rectangles produced from the rough casting cores. Can't see any obvious way of generating accurate cut-outs with rectangular corners in the mill. My milling cutters will all leave rounded corners (obviously!), even the smallest. Filing would, perhaps, be an option were it not for the fact that my results would be rubbish, Any pointers, p;lease?

Rgds

Bill

[Cornish JackParticipant @cornishjack]

[Michael GilliganParticipant @michaelgilligan61133]

Bill,

That's exactly what a DieFiler was designed for

May I suggest you have a look at the ongoing thread.

MichaelG.

 

Edited By Michael Gilligan on 30/09/2012 14:51:16

[Michael GilliganParticipant @michaelgilligan61133]

Alternatively, you could Broach the corners with a square tool …

MichaelG.

 

P.S.

Could you please post some pictures of the parts in question.

Thanks

Edited By Michael Gilligan on 30/09/2012 15:11:13

[Bruce VoelkerdingParticipant @brucevoelkerding91659]

Bill,

in such a situation, I would mill the opening as you mention, Then I would clamp a steel bar to each side of the steam chest in the bench vice (horizontal). The bars would be aligned to the machined opening. They will act as guides to limit the file's cutting depth. I have done this just recently. I guess if you are really unsure of your filing, you could also clamp a set of bars vertically in the corner you are filing. These bars would be clamped with a toolmakers clamp.

If you are really worried, you could machine two plates with an internal corner (or two corners to do one side of the steam chest at a time) and use as described above.

Bruce

[JasonBModerator @jasonb]

First question is do the corners need to be square, if teh slide vale does not go completely end to end then the couner can be left as is or possibly round the corners of the slide valve. Like this

 

You can also take the majority out with a reasonably stout milling cutter and then switch to a small dia to do the corners which will leave little to file away.

Best option for square corners in the mill is a slotting head, if you don't have one you could make a suitable cutter and plane out the corners using the quill handle.

Or better still just treat it as filing practice if you don't try your filing will never get better

 

J

Edited By JasonB on 30/09/2012 15:50:26

[John Stevenson 1Participant @johnstevenson1]

Bill seeing as it is a casting it will be cast iron or bronze, both soft metals so I'd advise to mill out with whatever tool is suitable which will leave the radiused corners.

Then make an aror up to hold a piece of square HSS and with the spindle locked on the mill use the quill as a slooter and carefuly remove the corners.

 

However this then promps to to ask does the design actually need square corners ?

Does the slide valve actually reach the corners and if so or close can the slide valve have a radiused corner for clearance ?

 

Not all designed are designed with easy machining operations in mind.

 

John S.

 

[EDIT] Jason beat me to it.

Edited By John Stevenson on 30/09/2012 15:52:41

[Cornish JackParticipant @cornishjack]

Many thanks gentlemen. Lots of food for thought there. I like Bruce's suggestion – 'cos i was thinking along those lines already … maybe a couple of pieces of gauge plate, hardened?

Michael – Ah, yes I actually have a die filer but haven't yet ventured into using it!!!

Jason and John … More blushes!! The answer is … I don't know!! I haven't built one of these previously and the plans are simply individual components with dimensions. I'm not at all sure how the bits fit together, leastways the 'internal' ones. I'm just making holes and swarf one bit at a time, to end up with a 'kit of parts'. It's good machining practice but not likely to end up as a thing of beauty – or, necessarily, functional! I have managed to 'lose' what I assumed was the valve casting (sort of bronze 'Toblerone' type thing) – presumably that shape is significant but I cannot see why

If I manage to generate the required shapes and fit them together, I'll post piccies (suitably out of focus!)

Rgds

Bill

[JasonBModerator @jasonb]

Try not to use hardened guide pieces, if you touch them with teh file it will get blunt rather quickly.

You should be able to cut another valve from solid without too much trouble.

J

[Sub MandrelParticipant @submandrel]

It isn't hard to file the corners square by had, as you have two edges to guide you.

A valve cavity with rounded corners will work fine, but if you want perfection make (file!) a square hole in some (e.g. 1/16&quot sheet brass and silver solder it onto a brass block. Now make the rest of teh valve measuring from the edges of the cavity – works a treat!

Finally, as long as the width of the valve cavity and ports are accurate and the valve doesn't foul the valve chest everything will work fine. The bigger the valve chest, the better, but only in terns of maximising efficiency. And no-one is going to be able to see with teh valve cover on anyway

Neil

[NJHParticipant @njh]

Hi Bill

You say – "Filing would, perhaps, be an option were it not for the fact that my results would be rubbish"

I recognise the dilemma but it seems to me filing is not a skill we are born with and all must learn through practice Some find the process theraputic but, for myself, if there was more filing needed in ME I would probably take up stamp collecting or somesuch instead. I've never been good at filing and I resort to rounded corners whenever I can get away with it!

N

 

Edited By NJH on 30/09/2012 21:25:00

[Cornish JackParticipant @cornishjack]

Thank you Jason – caveat noted, so preferred option No1 is no good!

Neil – that sounds encouraging … do you know of a suitable primer (on line) which explains the principles of steam valve operation?

NJH – you, Sir, are a man of impeccable judgement and to be heartily commended for your pragmatism

Rgds

Bill

[Trevor Drabble 1Participant @trevordrabble1]

Bill, Would like to offer the following suggestion. Since you dont especially need square internal corners, simply get rid of them. Fill the steam chest with an interference fit block of hardwood. Then carefully approach from above with a small diameter slot drill, with its centre directly over each corner point in turn. The block may then be removed since its function was to reduce the side stresses on the slot drill. Continue with the machining of the 4 sides of the chest as normal. You will then have an undercut in each corner which will allow the valve to fully enter the corner without interference.

Have drawn a simple sketch to explain. Not computor literate, so cannot get it onto these pages. If you supply me with your details, I will try and email direct, should you so desire.

Trevor.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Bill ,

Where 'square ' internal corners are needed for practical reasons , as to provide clearance for a moving part , rather than for aesthetic reasons it is much easier to drill a small hole at each corner – centred on where your notional scribed lines would cross – and then mill straight lines in between . You can choose to use a tiny hole which may leave a small cusp needing dressing away or a larger hole which will leave no cusp .

Where metal removal amounts to dressing off small amounts rather than bulk metal removal you will find that small scrapers work much more cleanly and are easier to control than small files .

Little details in engineering design – even this little matter of internal corners – can sometimes make a huge difference to the effective working of complex equipment in full size .

Regards ,

Michael Williams .

[Cornish JackParticipant @cornishjack]

Trevor – thank you for your suggestion. As I understand it, it appears to be similar to Michael's corner drilling (for which, also thank you). If I ever manage to find out what the fitting requirements for this valve are – i.e. sliding, surface contact, interference etc., I will give it a whirl. The engine is intended to be a twin vertical cylinder and there are TWO steam chests. However the plan sheet specifies only ONE of the 'Toblerone' shaped valves. Being a 'bear of little brain' this leaves me much confused (state normal!) The probable moral of this tale is – don't buy part (badly) machined casting sets for items which have no web access references. The only info I've found on the web for this engine are a couple of small pics – not a lot of help.

Onward and, probably. downward to the rubbish bin!

Rgds

Bill

[Ian S CParticipant @iansc]

Was there perhaps enough metal in the Toberon shaped bit to be cut in half to make the two valves.

Unless square corners are essenial, leave them,pehaps use a reduced size end mill to give a small radius, because its going to be difficult squaring the corners of the valve cover any way, I'v done it with a little chisel, but the valve in the photo has round corners, so why worry. Ian S C

[JasonBModerator @jasonb]

Ian that valve in my photo was to show that rounded valves could possibly be used its not teh actual Engine.

 

Bill, The Tiny Power Kits are now done by Rappahannock Boat Works I assume you have the 2V-10 which is very similar to a Stuart D10 which you should be able to find plenty of references for which will help you with the build. Harrold Hall has a good build guide to the singel 10V which uses mostly teh same parts.

J

 

Edited By JasonB on 01/10/2012 13:03:48

[Cornish JackParticipant @cornishjack]

Ian and Jason, thank you.

Re. Rappahannock, I've been in contact with them and purchased some replacement bits – excellent service. Unfortunately there is a dearth of build info on this engine but your pointer to HH's Stuart guide is most welcome – hope it will explain, if nothing else, just WHY this valve thingy is shaped like Toblerone

Rgds

Bill

[RICHARD GREEN 2Participant @richardgreen2]

Surely a small shaper or a slotting head on the mill would be ideal for these sort of obscure machining jobs ?

Richard.

[NJHParticipant @njh]

Maybe Richard but how many folk have either small shapers or slotting heads?

N

[Michael GilliganParticipant @michaelgilligan61133]

Posted by NJH on 02/10/2012 14:38:38:

Maybe Richard but how many folk have either small shapers or slotting heads?

N

It's stretching the definition a little, but;

anyone with a saddle, or top-slide, or tailstock on their lathe.

MichaelG.

[RICHARD GREEN 2Participant @richardgreen2]

We've all cut keyways in pulleys and gears at sometime or other by using the lathe saddle and winding the tool in and out of the workpiece, which is held in the lathe chuck.

You don't need a shaper to get the "shaper" action.

Richard.

[NJHParticipant @njh]

Of course Michael & Richard – sorry brain disengaged!

So Shaper, slotting head or lathe then!

N

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