Honing gunmetal cylinders

[Bob LambParticipant @boblamb44747]

[Bob LambParticipant @boblamb44747]

I would be really grateful for some advice on cylinder hones. There are quite a few of them on ebay. I am looking at one with three stones on springy arms. It also has an adjustment spring on the central rod which presumably is to increase the pressure on the stones. Are they suitable for model steam engines? How do you use them? What speed should you use? Do you lubricate them and, if so, what with? Any advice gratefully received. Thanks in advance – Bob

[Fowlers FuryParticipant @fowlersfury]

Bob.,
For what it's worth – and no doubt very little:-
I used one of the 3 armed hones you're describing. I ran it at slow speed (maybe < 200rpm?) and used a light machine oil diluted with paraffin. The GM surface seemed to be removed quite quickly particularly when new.
However, I'm far from convinced it should ever have been done. The between centres boring bar was a heavy one and the surface produced looked and felt pretty good. Moreover I was confident it had produced a parallel bore.
Those hones by contrast can (will?) very easily produce a bell mouth at either end of the bores as you need to keep them moving axially. So when the stones reach the end of the bores, you must be sure to reverse their direction or their springs will begin to push the stones angularly giving the bell mouth. Obviously the hones must never be allowed to dwell in one position.
On balance, I'd rely on a good finish from a solid boring bar for GM cylinders.

[JasonBModerator @jasonb]

I use the 2 and 3 stone brake cylinder honed of most of my cylinders. I put the hone in the drill press and run at about 500rpm holding the cylinder in my hand and gently moving it up and down. Paraffin to lub and it also stops the stones getting clogged. As said just let the stones start to come proud of the cylinder ends before moving the cylinder back the other way.

[Bob LambParticipant @boblamb44747]

FF and Jason – thanks for your replies. I think I will try one and give it a go on an old cylinder and see what sort of result I get. Thanks again – Bob

[ken king, King DesignParticipant @kenkingkingdesign]

Hello Bob, you may find this useful in achieving the surface finish you seek. I used it to polish some bores, using green buffing compound mixed with a little oil, but equally well you could use a different compound, such as superfine grinding paste if you are after a micro-scratch oil-retaining surface. A very short description can be found by searching for 'quick and effective bore polishing mop'.

It comprises adhesive backed draught excluder and (in this case) a piece of broom handle, turned to about 3/16" smaller diameter than the bore. Spin the mop at modest speed in the lathe or drill, and feed the casting back and forth by hand, making sure of course that the mop is not too tight a fit.

[ken king, King DesignParticipant @kenkingkingdesign]

Hello again Bob. Annoyingly, unless one knows titles reasonably accurately, nothing comes up. I should have given you 'Quick,easy and effective bore polishing mops'. Hope this helps,

Ken

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ken king, King Design on 25/01/2018 11:00:01:

Hello again Bob. Annoyingly, unless one knows titles reasonably accurately, nothing comes up. I should have given you 'Quick,easy and effective bore polishing mops'. Hope this helps,

Ken

.

For info. … Putting that title, or indeed the previous approximation, into the search box on the home page works fine, and locates: **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=87538

MichaelG.

 

Edited By Michael Gilligan on 25/01/2018 11:14:16

[Neil WyattModerator @neilwyatt]

The search box above is very literal and looks for an exact match, so short phrases work best.

'polishing mop' works.

[JasonBModerator @jasonb]

Does the mop not give more of a lapped finish that the Honed one the OP wanted? Also can't see how it would take off any high spots from the cutting tool

[Clive HartlandParticipant @clivehartland94829]

The 3 hone laps can be bought from car tool accessory suppliers, I have seen 3 sizes and come with a spare hone. Unfortunately I have disposed of my car tool catalogue and cannot remember the name!

Clive

[ken king, King DesignParticipant @kenkingkingdesign]

I didn't think the objective of honing was to remove high spots, that's essentially re-machining. I understood the honing process was to change the nature of the surface finish, usually (as in car cylinders) to help retain an oil film. In that case, the mop charged with a suitable compound will do the job.

[IanTParticipant @iant]

I found myself wondering about the real difference between honing and lapping. From American Machinist;

"Honing is a low-velocity abrading process. Material removal is accomplished at lower cutting speeds than in grinding. Therefore, heat and pressure are minimized, resulting in excellent size and geometry control. The most common application of honing is on internal cylindrical surfaces. The cutting action is obtained using abrasive sticks mounted on a metal mandrel. Since the work is fixed in such a way as to allow floating, without clamping or chucking, there is no distortion."

"The principal use of the lapping process is to obtain surfaces that are truly flat and smooth. Work that is to be lapped should be previously finished close to the final size. While rough lapping can remove considerable metal, it is customary to leave only 0.0005 in. to 0.005 in. of stock to be removed. Lapping, though it is an abrasive process, differs from grinding or honing because it uses a ”loose" abrasive instead of bonded abrasives like grinding wheels. "

​However, I think I would actually describe KKKDs method as being a form of polishing (an internal 'mop' ). However, whatever we call the different processes and however they work, in this case (if they produce a satisfactory end result) it probably doesn't matter too much – being a matter of what suits the machinist best.

Regards,

IanT

 

Edited By IanT on 26/01/2018 10:02:24

[Fowlers FuryParticipant @fowlersfury]

Some useful advice offered for the OP (Bob) but he didn't tell us what his cylinders were made of, or the piston rings he intends to use (polymeric? PB? CI? stainless?). If his bores are GM, then my opinion remains that honing with such devices may do more harm than good in inexperienced hands (e.g.easy to bellmouth and/or taper, embed particles from hone etc).
If his bores & rings are CI and the boring bar has left high spots, then honing with such devices may certainly be worthwhile. One of the limitations of vitrified abrasive stones is that they wear rapidly. It is claimed that depending on the grade of stones and hardness of the bore, (quote) "the operator must compensate for stone wear to keep the bores straight otherwise it will lead to tapering". How one can do that is not explained. Examination of those "cheap" devices doesn't instill confidence that each ofl their stones will exert the same wall pressure or that the stones themselves are flat.
Though with few us having Delapena honing machines, they're maybe better than nothing – if really needed.

[Ian S CParticipant @iansc]

I don't think a honed surface is what is needed on a gunmetal cylinder, it leaves a micro grooved criss cross that retains oil which is good for a cast iron or steel bore with cast iron rings.

I use an expandable wooden mandrel with grinding paste to lap the bore of my hot air engines as suggested by James G. Rizzo.

Ian S C

[JasonBModerator @jasonb]

Posted by Fowlers Fury on 26/01/2018 10:03:39:

Some useful advice offered for the OP (Bob) but he didn't tell us what his cylinders were made of

There is a clue in the title of the thread

[Fowlers FuryParticipant @fowlersfury]

"There is a clue in the title of the thread"

Put it down to senility……….

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