1/4 Scale merlin project - allowance for honing

[Lloyd W]

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.

 

[gbritnell]

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.

 

[byawor]

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

 

[mayhugh1]

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

 

[Lloyd W]

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

 

[Actionman]

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]

Of course, but its a lot of work, means 2 setups and consequent reduced concenticity between inner and outer diameters.