1/4 Scale merlin project - allowance for honing

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Lloyd W

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A very good day to you all,

The cylinder blocks and crank case now largely completed I am turning my thoughts to the cylinder liners.

These I will make from 4130 seamless steel tube in the annealed state. My first tests seem to show this material to be quite readily machineable.
I know this kind of question chases its own tail, but assuming I can obtain a good shiny smooth turned surface for the bores of my liners, how much allowance on a nominal DIAMETER of 1.35 inch would you consider I should leave for honing.
As I have no real experience in these things I would very much appreciate your advice and comments

Many thanks
Lloyd.
 
Honing should do no more than polish the bores. A good surface finish from machining should leave surface imperfections no more than several tenths high so .001-.0015 should be more than enough. If you have to take off .003-.004 to smooth out the surface then your boring isn't very clean.
 
You don't say what tooling you have for honing but if you are thinking a
brake cylinder hone I doubt you will get the required results specially since you need 12. If it was me I would bore then ream 1/2 thou under (assuming you have the ream)then take them
to a shop with a Sunnen hone.
Bob
 
I used an Acro barrel lap and 600g lapping compound to finish mine. One to 1-1/2 thousandths is a max to leave for lapping. Any more and it's a long messy weekend. You'll want to lap and measure a little off each liner (keeping track on a written record) to help insure they all come out the same. Lap as required to get them identical as soon as possible, and then continue as needed to get them all to the target value at the same time. Be careful to not let one get away from you so you'll have to lap all the others to match. It's a good idea to start out with a couple extras in case this happens. - Terry
 
Thankyou Gentlemen for taking the time to reply.
Your advice, from your experience is extremely valuable.

My small lathe will not accomodate reamers of the bore size, so I will continue with single point tools for the boring and outside dimensions.
For that my machining tests lead me towards brazed carbide with oil coolant. I had a set in a bottom draw, now promoted to a top drawer!!
I think these when sharp, will remain so and give me the best chance of dimesional control on the diameters.

I will keep you posted in due course about the results.

BTW I just wanted to add here that my hat is off to Terry Mayhugh (above), who I know has built and run a version of this engine.
I hope, one day, to be able to say the same.

Wishing you all a good day,
Lloyd
 
My small lathe will not accomodate reamers of the bore size, so I will continue with single point tools for the boring and outside dimensions.

Could you put the reamer in the lathe chuck and make a fixture to mount the barrel on the saddle?
 
Lloyd W said:
My small lathe will not accomodate reamers of the bore size, so I will continue with single point tools for the boring and outside dimensions.
Click to expand...
Lloyd, you cannot get a good enough finish with a reamer, instead you will need to lap them, turn them to about 1 to 1.5 thou undersize then lap them to right on. you can usually get an acceptable lap using an "Acro Lap", but if you want perfection use a "Helical Lap". Peter.
 
Peter,
Yes I agree, the reamer idea is off the table. I've done some machining tests and now bored and turned one liner. I'm fairly happy with the result, the bore is smooth and regular about as you say 1.5 thou undersize. If I can do one I should be able to do another - good since I have 12 or 13 more to make with spares.
I'm not ready to hone yet, in fact I'm looking ahead to purchase a good lap.
Acro USA would do the job but they dont have the size I need in stock, and with postage etc to Europe it gets expensive.
I'm looking for a similar European supplier. Who would supply the helical lap that you refer to?
I appreciate your comments, thanks, Lloyd
 
Lloyd W said:
Peter,
Yes I agree, the reamer idea is off the table. I've done some machining tests and now bored and turned one liner. I'm fairly happy with the result, the bore is smooth and regular about as you say 1.5 thou undersize. If I can do one I should be able to do another - good since I have 12 or 13 more to make with spares.
I'm not ready to hone yet, in fact I'm looking ahead to purchase a good lap.
Acro USA would do the job but they dont have the size I need in stock, and with postage etc to Europe it gets expensive.
I'm looking for a similar European supplier. Who would supply the helical lap that you refer to?
I appreciate your comments, thanks, Lloyd
Click to expand...
"helical lap" is the name of the company and you buy directly from them and that's all I use (along with their 1200 grit alumina abrasive), I do have some from "acro lap" but don't really use them as they aren't long enough and their adjustment creates a barrel shape so hard to get a perfectly straight liner with them.
 
Guessing this is the website you are referring to & even a nice little animation. I've had their website saved in my Favorites but have yet to try one. Something tells me from an inquiry a long time ago they were $$ but that may be a function of where I'm located.

Peter, what alloy of lapping barrel do you use? (Or is there any choice?)

https://www.helicallap.com/tool-fundamentals/
 
petertha said:
Guessing this is the website you are referring to & even a nice little animation. I've had their website saved in my Favorites but have yet to try one. Something tells me from an inquiry a long time ago they were $$ but that may be a function of where I'm located.

Peter, what alloy of lapping barrel do you use? (Or is there any choice?)

https://www.helicallap.com/tool-fundamentals/
Click to expand...

AFAICT you can only get "helical lap" brand in cast iron, all of mine are.
if you're trying to save $$$ you might be in the wrong hobby :) !!!
(for example you can't save $$$ by buying a cheap tap :-( !!!)
 
petertha said:
Guessing this is the website you are referring to & even a nice little animation. I've had their website saved in my Favorites but have yet to try one. Something tells me from an inquiry a long time ago they were $$ but that may be a function of where I'm located.

Peter, what alloy of lapping barrel do you use? (Or is there any choice?)

https://www.helicallap.com/tool-fundamentals/
Click to expand...

That is the first time I have seen that gizmo.
Learn something new every single day.
.
 
byawor said:
You don't say what tooling you have for honing but if you are thinking a
brake cylinder hone I doubt you will get the required results specially since you need 12. If it was me I would bore then ream 1/2 thou under (assuming you have the ream)then take them
to a shop with a Sunnen hone.
Bob
Click to expand...
God advice.
 
Look for a Sunnen SNJ-10 portable hone. The min bore for that model is 1.25". I'd leave 0.002" for honing and try to get all cylinders as close to the same as you can. I have a Lisle 16000 hone, but its smallest bore is around 1.75".
 
Lots of people swear by those little honing tools that are made for car brake cylinders. Personally I don't really trust them so I always make my own lapping tool. Even if a lapping tool is not perfectly cylindrical it will tend to become so with use and my results so far have always been very nice. I used diamond paste but carborundum also works well. A good expanding lap also doubles as a handy mandrel.

With regards to turning tools can I suggest obtaining a few polycrystalline diamond inserts from somewhere like ali-express. They are quite cheap and my experience has been that they produce an amazingly good finish. They are very brittle though so save them for finishing cuts and treat keep them away from the stress such as the center of a facing cut.
 
petertha said:
Guessing this is the website you are referring to & even a nice little animation. I've had their website saved in my Favorites but have yet to try one. Something tells me from an inquiry a long time ago they were $$ but that may be a function of where I'm located.

Peter, what alloy of lapping barrel do you use? (Or is there any choice?)

https://www.helicallap.com/tool-fundamentals/
Click to expand...
I prefer a lap that is barreled. A parallel lap risks bell-mouthing the job because it is impossible to hold the job dead straight and because the slurry accumulates at the ends. With a barreled shape it is also easier to feel tight spots.
 
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