Machining Allen cylinders

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Machining Allen cylinders

Post by crackerjackhoghead » Mon Sep 19, 2011 2:02 am

Can you guys give a novice machinist some idea how to go about machining my Allen Mogul cylinder castings? In what order do I do what? Some pictures of machined cylinders would be worth a thousands words. If this has already been hashed out then please point me to the thread.


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Re: Machining Allen cylinders

Post by Fred_V » Mon Sep 19, 2011 7:08 am

i like to do it in the lathe using a 4 jaw chuck. center up what will be rear end facing out. you want the rear end faced off square to the bore so do them both in one set up. turn it around to face the other end. get a 3/4" boring bar with carbide inserts.
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Re: Machining Allen cylinders

Post by Harold_V » Mon Sep 19, 2011 2:42 pm

Fred_V wrote:get a 3/4" boring bar with carbide inserts.
Use the proper grade insert. Cast iron can be challenging, due to chilling and/or sand deposits. C5 carbide is not a good choice. C2 is.

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Re: Machining Allen cylinders

Post by crackerjackhoghead » Mon Sep 19, 2011 3:24 pm

So do I bore and face the cylinder first and then machine the valve surface? Do a turn the outside diameter of the cylinder ends? Do I mill the valve "block" to length or face the ends of it in the lathe or leave it as it is?

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Re: Machining Allen cylinders

Post by 10 Wheeler Rob » Mon Sep 19, 2011 3:45 pm

I rough machined the ends and valve face and side that mounts against the saddle. leaving about 0.050 to 0.100 inch finish alowance.
Then set it up in the four jaw and bored with a 3/4" carbide insert borring bar and machined the faces, bore, and OD of the ends. Changed the insert to fresh point for the last few light passes to get good surface finish. It took a lot of set up time for me in the four jaw to make sure it was in squar and the bore was centered where it should be. The bore was done a couple of thousands under size, and carefully honed with an automotive brake hone, measuring often so as not end up with it tapered or bell mouthed.

Finish machined the out side surfaces with a carbide fly cutter set up in 6" vice and aligned parallel to the bore, and machined to 5 thousands oversize. Machined drain passages and ports. Drilled and tapped the ends and steam chest side. Surface ground the valve side and saddel side, with very light passes to final dimension.

More experanced machinist would probably recomend hand or machine lapping/honning would be more apropiate for the bore final finish and valve surface. But not everyone knows how or has access to that kind of equipment and lapping plates.

The stock iron rings form Allen Models run nice and smooth when I finished.


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Re: Machining Allen cylinders

Post by Greg_Lewis » Mon Sep 19, 2011 8:32 pm


I did mine in an Atlas 12-inch lathe, which is not known for rigidity (I can make a dti on a piece of chucked stock wiggle by pushing on the headstock with my hand). I’ve put up partial remains of an old website that included some pix.

You can click on each photo for a larger view, which also includes explanatory cutlines.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 30 years of turning perfectly good metal into bits of useless scrap.

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Re: Machining Allen cylinders

Post by Kimball McGinley » Tue Sep 20, 2011 7:54 pm

Since the rear face has to be perfectly square to the bore, they are done in the same set-up, as all said above. Just remember to identify which is which! I made a centerpunch mark and later drilled it in a little and then filed it flat to mark the rear face. I did it right in the lathe.
Also you may have to to make left and right sides and don't mix them up either!

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