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Oil grooves in piston valves

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SpringbokB116/09/2011 05:59:54
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4 forum posts
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I am having difficulty turning 1/64" wide grooves by 1/16" deep in 7/8" diameter stainless steel. Ten such grooves are called for in each of the piston valves required in Martin Evans 5" gauge Springbok. I've tried grinding down HSS lathe tools and made a holder for tools made from hacksaw blades. In both methods the very thin cutter very soon breaks. Is there a better method?
john kennedy 116/09/2011 07:16:42
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214 forum posts
24 photos
It's a long time ago now but I'm sure I did mine with a hacksaw blade. Very slowly and with very little overhang. How about a slitting saw fixed in the toolpost,might be stronger ?
If that fails dont go so deep,they are only to hold oil,and no one will know...
Clive Hartland16/09/2011 08:41:34
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2929 forum posts
41 photos
Do the grooves have to be flat bottomed, surely as oil grooves then a 'V' groove will suffice.
You have not stated the type of stainless you are using, perhaps a free machining type would be better.
Its a long time since I machined stainless and I cannot remember the grade that machined freely! 303 and 316 spring to mind but I had no problem machining circlip grooves in them!
 
Clive
Richard Parsons16/09/2011 10:13:27
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645 forum posts
33 photos

Hi,


Here is a trick that might be better. The old man used to get a regular call out to farms where the vacuum pumps on the milking machines were forever seizing up. The eventual solution he used was to skim the rotary pump bore about 0.003” oversized then he used a fine diamond pattern knurl. This of course reduces the diameter of the bore. He made adrift which was hardened ground dead to size. The drift was pushed through the pump bore making it dead to size which had a fine net like pattern which acted as an oil reservoir. Result no more seizures.


Ok machine the piston valve 0.002” undersize, lightly knurl it and then make a ‘die’ which has a lead in taper with the rest ‘dead to size’. Push the piston valve through the ‘die’. You will get a very good oil retaining surface.


Rgds


Dick

Gary Brooke16/09/2011 10:54:30
28 forum posts
Hi
I would be interested on how you get on. For when I get to that stage. Some time off
Regards Gary
Gary Brooke16/09/2011 10:58:56
28 forum posts
Hi just hade a brain wave after last post would it be possible to screw cut the groves ?
Regards Gary
Ian S C16/09/2011 11:16:16
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7468 forum posts
230 photos
I use the same system on the power pistons on my hot air engines, I make the grooves no deeper than .010" X .030 wide using a thread cutting tool. Mine are in cast iron, but I see no problem with stainless, just go slow, and do it to depth in one cut. If you have trouble you might try a suitable carbide tip, but you should'nt need too. Ian S C
GoCreate16/09/2011 13:17:46
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387 forum posts
119 photos
303 is the free cutting grade of st st, machines very easily compared to 316 and easily polishes to a mirror finish.
 
If you want to stay with the drawing dimensioins of 1/64 wide a 1/16 deep another method might be to mill them using a slitting saw in the mill. Put the part in a chuck on a rotary table, feed the slitting saw to cutting depth and slowly rotate the table.
 
Nigel

Edited By tractionengine42 on 16/09/2011 13:18:13

Ian P16/09/2011 21:09:53
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2747 forum posts
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I dont know much about steam engines but the groove proportions dont seem ideal to retain oil. If they do retain oil (by capillary action?) then surely the oil will stay at the deepest part of the groove?
 
As someone previously, suggested shallow 'V' grooves would seem more appropriate.
 
If the grooves have to conform to the drawing then machining them with a parting tool type blade is possible after a little trial and error to find the best combination of speed and feed. A slitting saw on a rigidly mounted (slow RPM) toolpost grinder would certainly work too.
 
Ian P
ady17/09/2011 09:03:59
612 forum posts
50 photos
Hi just hade a brain wave after last post would it be possible to screw cut the groves ?
----------------------------------
 
I did this with my drummond backgear repair which had to be very tight, but not break or turn when under pressure.
 
I bored undersize to a very tight fit then cut a shallow thread it it then battered it (carefully) onto the stem of the backgear.
Worked a treat.
 
For cutting a groove into hard stainless I would mount the stainless between centres then use a high speed milling attachment with a disc cutter.
Even careful use of a well mounted dremel on a milling slide would probbly suffice.
Ian S C17/09/2011 13:09:59
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7468 forum posts
230 photos
Grinding could be done by mounting a Dremmel type tool on the tool post, and use a cut off wheel, But as Ian P says, and I agree the grooves seem too big, mind you with the hot air engines I want the minimum amount of oil. Ian S C
SpringbokB122/09/2011 01:40:38
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4 forum posts
28 photos
Some days ago I wrote a message thanking all who contributed suggestion to resolve my problem. I don't see it here so I'll try again . I am pondering the various options offered and feel considerably more confident that I shall eventually achieve the required result. I will post again when I get there.
 
I think the response was quite amazing.
Dusty22/09/2011 10:00:01
498 forum posts
9 photos
I would advise caution if 'screwcutting' your oil groove. You would be basically connecting the inlet and exhaust with your oil groove, it of course depends on how deep the groove is, if, or how much effect it has on the running of the loco. The basic concept is good provided that the groove does not connect the two chambers. I would start the groove from an annular ring 1.5mm fron the end of the valve head screwcut the groove and stop 1.5mm from the other end, do not withdraw the tool you will then have an annular ring at that end. This will prevent steam passing by the valve head.
Ian S C22/09/2011 11:16:19
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7468 forum posts
230 photos
Dusty that is quite a good idea, but as the grooves do not need to beat a uniform spacing, separate groves are easier, its just a few seconds work, I do the groovesjust before I do the finishing cut on the diameter of the piston, because when I do them I usually push up a bit of a burr on the edge of the groove. Ian S C
Springbok26/09/2011 04:00:37
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879 forum posts
34 photos
Will send you a pic and details now off to do a bit to pay the bills. only spotted your posting by accident
 
regards
 
Bob
Springbok27/09/2011 06:39:09
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879 forum posts
34 photos
--
Still trying to work out how to put a pic on this thread
 
Quote 28th April P517 The oil grooves being put in with an old hacksaw blade high-speed for preference before the final overall cut is taken.
 
I case hardened my blade but that could be OTT.
 
I have a complete set of the articles (photocopies) as our club which is over a 100 years young has a complete set from vol 1 of MEngineer in our library. I have decidied to scrap the reverser design that Martin Evans put in his drawings for I think simplicity and will be makeing an more accurate representation. could I refer you to Chris Vines free ebook which refers to this item It is worthwhile looking at his Bongo.
 
Please keep in touch as one B1 builder to another.
 
Bob
 
 
Springbok27/09/2011 06:56:21
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879 forum posts
34 photos
Oh please watch out for loads of missing holes not in the drawings and it was april 28th 1960.
 
bob
Gary Brooke27/09/2011 13:35:00
28 forum posts
Hi Bob
I see that you have found missing holes on the drawings.Please will you enlighten me before I get to far into the build.also what sort of reverser are you going to use.
Regards
Gary
KWIL27/09/2011 18:55:48
3681 forum posts
70 photos
You can buy tip tool vertical inserts that cut 0.5mm wide, I use them for narrow relief against the end of a turned down cut to ensure that the end does not have a tool radius left. Look in J&L Catalogue and others.
Springbok27/09/2011 21:43:05
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879 forum posts
34 photos
Hi Kwil
looks a good source will keep it in mind
Thanks
 
Hi Garry
Please look at
it will give you a pic of what it should look like
also try
 
Will post tomorrow all that I have found so far
 
Bob
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