Oil grooves in piston valves

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Oil grooves in piston valves

This topic has 23 replies, 12 voices, and was last updated 17 December 2011 at 19:30 by SpringbokB1.

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16 September 2011 at 05:59 #74983
SpringbokB1
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@springbokb1
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?
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16 September 2011 at 05:59 #1034
SpringbokB1
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@springbokb1
16 September 2011 at 07:16 #74986
john kennedy 1
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@johnkennedy1
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…
16 September 2011 at 08:41 #74988
Clive Hartland
Participant
@clivehartland94829
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
16 September 2011 at 10:13 #74993
Richard Parsons
Participant
@richardparsons61721
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
16 September 2011 at 10:54 #74999
Gary Brooke
Participant
@garybrooke63895
Hi
I would be interested on how you get on. For when I get to that stage. Some time off
Regards Gary
16 September 2011 at 10:58 #75000
Gary Brooke
Participant
@garybrooke63895
Hi just hade a brain wave after last post would it be possible to screw cut the groves ?
Regards Gary
16 September 2011 at 11:16 #75003
Ian S C
Participant
@iansc
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
16 September 2011 at 13:17 #75013
GoCreate
Participant
@gocreate
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
16 September 2011 at 21:09 #75030
Ian P
Participant
@ianp
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
17 September 2011 at 09:03 #75042
ady
Participant
@ady
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.
17 September 2011 at 13:09 #75048
Ian S C
Participant
@iansc
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
22 September 2011 at 01:40 #75252
SpringbokB1
Participant
@springbokb1
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.
22 September 2011 at 10:00 #75261
Dusty
Participant
@dusty
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.
22 September 2011 at 11:16 #75265
Ian S C
Participant
@iansc
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
26 September 2011 at 04:00 #75419
Springbok
Participant
@springbok
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
27 September 2011 at 06:39 #75448
Springbok
Participant
@springbok
—

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
27 September 2011 at 06:56 #75450
Springbok
Participant
@springbok
Oh please watch out for loads of missing holes not in the drawings and it was april 28th 1960.

bob
27 September 2011 at 13:35 #75465
Gary Brooke
Participant
@garybrooke63895
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
27 September 2011 at 18:55 #75487
KWIL
Participant
@kwil
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.
27 September 2011 at 21:43 #75491
Springbok
Participant
@springbok
Hi Kwil

looks a good source will keep it in mind

Thanks

Hi Garry

Please look at

http://www.petersrailway.com/e-book.aspx

it will give you a pic of what it should look like

also try

Model Engineering Clearing House

Will post tomorrow all that I have found so far

Bob
27 September 2011 at 23:12 #75496
Springbok
Participant
@springbok
Hi Garry

Firstly if you look at the drag beam there should be holes for the vacume pipes etc; this is shown in drawing 8

Watch out for your running boards before you assemble them there are slots for the oil lubricator, and other items. BUT not convinced this is where it should be doing more research. The steam injector pipe is at the wrong angle but not a lot we can do about this if we have purchased reeves etc; castings.

Other comments;

The cut outs in the main frames for the boiler blow downs need to be about 1/2″ further up and about 1/8″ further forward. The reamed 3/16″ hole near the front coupled wheel should be 7/32″ . There are 2 different boiler drawings in circulation. The one you want has the girder stays on top of the fire box wrapper attaching to the outer shell of the boiler. Check the thread sizes of the boiler fittings agree with the thread sizes for the boiler bushes. The steam manifold is shown twice with discrepancies in the measurements

One correspondent tells me that the bogie frames are too short on the drawings. Worth checking before you cut metal.
From an email.
Someone else (sorry, I forget who it was) said the following:
The boiler is pitched .375″ too high, this makes the cab height out of scale. On the full size engine there is virtually no gap between the frame and boiler. The cab and running boards are approx .75″ too wide as is the tender. I have seen one built using Martins drawings but scaled correctly, a big improvement on mine. Have no fear though, it is fairly easy to build and steams and pulls like a good’n. If you have an old set of drawings you may find a stretcher trying to fit between the frames where the middle tender wheelset sits. This corrected on later drawings.

I am going to try and get mine running on air next week so everything crossed

regards

Bob
28 September 2011 at 13:08 #75506
Gary Brooke
Participant
@garybrooke63895
Thanks Bob for all them comments lots to check. I know the drawings are not for a true scale model. Buy the way good luck with your air test
Regards Gary
17 December 2011 at 19:30 #79987
SpringbokB1
Participant
@springbokb1
I found a Canadian supplier who handles 0.5mm grooving cutters. They did the job for me although I broke quite a few in the process. They are not the cheapest piston valves! I will post a photo in my album.

Many thanks to all who responded to my query.

Nigel
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