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Honing bronze cylinder bores

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Tony Martyr09/01/2012 20:17:11
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I have experience of using (dry) 'flexihones' on car engine liners and 3-blade stone types (oil cooled) to finish hardened gear-wheels but i have never used any of the small hones such as those advertised as 'Cylinder Hone Kit 4-in-1' on bronze bores.
The LP bore ( 1 7/8" dia ) of the engine I'm building is not as good a surface finish as I would have liked but as it is very close to finished size I am considering honing both it and the other two cylinders.
Is this a normal process in model engineering?
I assume it would be an oiled process?
Tony
Phil P09/01/2012 20:49:45
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Have you considered "Lapping" it with an abrasive impregnated split lap instead ?
 
If it is already very close you should get a better finish with less chance of making it bell mouthed or barrel shaped.
 
Phil
Ady109/01/2012 20:55:43
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Delapena used to make good manual hones.
 
A search using that term might yield some useful results in here and on the netty.
Ramon Wilson09/01/2012 23:06:56
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Tony,
 
As suggested by Phil an aluminium or lead lap lap using carborundum grit will do the job perfectly with paraffin as a lubricant. Be wary of using diamond paste - so readily available now - as it will bed into the bore surface and is difficult to remove unless you have an ultra sonic cleaner. It depends on how bad the turned finish inside the bore is but the better you can turn it the easier it is to produce a good lapped finish. Bronze needs a razor sharp tool for those last cuts (hope I'm not teaching granny there)
 
As you're probably aware the three stone brake cylinder hone is really meant for breaking the surface into micro scratches rather than honing the surface true from a turned finish though it does work on cast iron albeit quite slowly. (Recently done a 27mm bore) It may work in your case but you may find the stones will load up and glaze over quite quickly on bronze.
 
Delapena hones are very expensive relative to a home made lap. I bought a machine near two years ago and still have very little tooling due to the expense.
 
Hope that helps some
 
Regards - Ramon
 
 
NJH10/01/2012 10:46:46
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Tony
 
I did use a cylinder hone ( from Polly Model Engineering ) to finish the cylinder of a vacuum engine. It produced a very good surface finish and was easy to use.
I arranged for the cylinder to be enclosed within an old plastic jar, centred the cylinder under the chuck if my pillar drill, and clamped it all to the table. The hone could be moved up and down freely in the bore whilst a plentiful supply of honing oil was applied ( and contained by the jar from flying around the workshop!) A slowish speed was used and it was easy to keep the hone moving back and forth with the drill press handle. It took a while to get the finish and very little metal was removed. The result was a very good finish with no bell-mouthing. This was, however, a cast iron cylinder - I'm not sure how this would work on bronze.
So all in all a successful outcome to my construction project - except I STILL can't get the blooming vacuum engine to run and I'm yet to find anyone who has!!
 
Regards
 
Norman
 
Ian S C10/01/2012 11:12:11
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For my hot air engines I use a wooden lap, I should get some courser grinding paste, the stuf I have is very fine(and cheap), Got 250gm pot yrs ago. Turn up a bit of wood, a firm fit in the bore. Cut a slit up half the length, make the lap about twice the length of the cylinder. To adjust the tightness either put a thin wedge, or a wood screw in the slot. Cover it with paste, mount it in the lathe, and turn it on sliding the cylinder up and down. If you need to use a finer paste you'll need another bit of wood, you can't clean the old one. Its cheap, tends to be a bit slow (maybe a good thing), proberbly not as accurate as a propper lap, but you can have what ever size you want. There is a grinding medium that self destructs, ie., breaks down and does'nt embed in the article being lapped, someone will come up with the name of it.    Ian S C

Edited By Ian S C on 10/01/2012 11:16:33

Ramon Wilson10/01/2012 13:32:21
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There is a grinding medium that self destructs, ie., breaks down and does'nt embed in the article being lapped, someone will come up with the name of it. Ian S C

Edited By Ian S C on 10/01/2012 11:16:33

Carborundum (silicon carbide) appears to follow this characteristic quite well but you do need to clean the part thoroughly between changing grit sizes.
 
I think the product you may be thinking of is 'Timesaver' which I believe has this property and is sold as such.
The problem with it is trying to source it in the quantities that we would want as 'home users' but if you find some in small quantities at reasonable cost I would be very pleased to hear about it.
 
I' ve never tried using wood Ian - would that have to be a good hard wood like beech or maple?
 
Regards - Ramon

Tony Martyr10/01/2012 17:14:01
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I think I am going to follow the method described by Norman (NJH) as it is very close to the way in which I used a large Delapena hone many years ago.
I had not considered Polly Engineering but found a quite good Technical Note on the subject on their web site.
The 'less than perfect' bore finish was produced by a boring-head mounted in my milling machine - because the casing was too large to mount in my Myford late. The HP bore which was machined in the lathe is perfect - the difference, I think, is because the boring head had to be fed by hand while the lathe was on a fine machine feed.
Tony
JasonB10/01/2012 17:34:25
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Ramon, you can by sets of the various grades of Timesaver which would be the best option for our sort of use.
 
They do both ferrous and non ferrous, available from here who do a lot of other stuff for the full size tarction engien boys & gals.
 
I've lapped bronze/GM cylinders with a hardwood lap, something reasonably close grained is best.
 
J

Edited By JasonB on 10/01/2012 17:35:45

Peter Bell10/01/2012 19:26:38
399 forum posts
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I would second that about "Timesaver" Use it on everything ferrous and non ferrous with really good results, beats all the carborundum type stuff.
 
Make some 6" dia pistons for a loco and everyone insisted on using conventional abrasives to lap the new piston to to the existing piston rod but this only produced scoring and ridges even with different grades. Used some timeasver and we got a smooth finish within minutes. A good thing is the way it become finer as you use it helping get a better finish.
 
Only downside is the cost but it certainly goes a long way---until your friends find out about it!
 
Peter
Ramon Wilson10/01/2012 19:46:16
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Thanks Jason - despite a good search some time ago I had not come across this supplier.
 
It's still a bit too pricey for me though - best part of 50 quid seems an awful lot to spend when I have oodles of silicon carbide in several grits which so far has worked very well in the I/C bores lapped so far. Just think how many small bores like these you'd have to do to use 3ozs - of each grit
 
'Rain check' time on this one then but thanks again.
 
Good luck with using the Polly hone Tony - I have had very good results using mine but so far have only used it on cast iron. Please let us know how it goes on the bronze
 
Regards - Ramon
Ian S C11/01/2012 12:49:59
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Thanks Ramon, Time Saver is what I was thinking of.
As far as the wooden hones go,my source of information does not say, but a fine grained, and hard wood (not necessarily hardwood) seems to be OK. Hardwoods are not too common in this part of the world (thats free by my way of getting the stuff).
I'v also used 2 and 3 stone brake hones, and I was wondering the other day whether one of those cylindrical flap wheels would be any use, maybe a bit too fast. Ian S C

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