Finned cast iron cylinder machining question

daryl bane · Aug 28, 2018

I have some replacement cylinders for an antique motorcycle engine. These cylinders do not have the pushrod tube channels. I will need to mill? these channels out and am scared to death of busting a fin. I figure a large ball end endmill should work, but don't know the best way to attack it.
Should I fill up the spaces in the fins with some sort of removable compound, plaster of paris? Or, chuck the whole idea and do it with a die grinder and alot of work? I will have to do some cosmetic work after the milling anyway, but seems the millling way would be more uniform.

HuFlungDung · Aug 28, 2018

Why not just drill the hole first? Then put your endmill to work with a drilling motion and just step your way out of the hole with modest cuts. Maybe I've visualized what you want to do incorrectly.

daryl bane · Aug 28, 2018

yep, you've got the idea right. Maybe use a center cutting end mill and bore the hole and then step it out one fin at a time. I am taking in all suggestions. Thanks.

HuFlungDung · Aug 28, 2018

When you get near the break through zone at the edge of the fins, I'd suggest you switch to a small endmill and mill each side separately, or else the chances of catching and breaking is pretty substantial.

tdmidget · Aug 28, 2018

Annular cutter, slow feed

Limy Sami · Aug 28, 2018

BTDT in a former life, I'd go the plaster of Paris and small endmill for the breakout route, those thin CI dins NEED support

Most acids will get rid of the plaster of Paris

thermite · Aug 28, 2018

tdmidget said:
Annular cutter, slow feed

Yup. I've got em. I'd use 'em. Drillpress. Not mill. Better "feel" as to what is going-on, gentler break-through, each successive fin.

I mought also do the Plaster of Paris anyway. Cheap as dirt, mere minutes for setup, ever so easily removed, so why would one not?

Chip clearance/evacuation - or lack thereof could be the major downside. But it was "Cast Iron", not shiney-wood, yah?

Ah.. I see Sami types faster.. or maybe just THINKS faster?

Gettin' old..

MihiT · Aug 28, 2018

Instead of plaster of paris, would it be feasable to drop the whole thing in molten lead. Make one big chunk which will support the fins and prevent any breakthrough, dampen the vibrations of machining.
Once done put it in a pan over a gas ring and melt the lead back out.
Never done it, just thinking out loud...

thermite · Aug 28, 2018

MihiT said:
Never done it,

I believe you.

Ask an Old Skewl Plumber about dealing with lead over Oakum joints, vertical drain/waste/vent Cast Iron lines.

Gots to keep in mind that all it took to modify CI was to snap off sections with channelocks.

Bending moment just is not its long suit.

Mud · Aug 28, 2018

Photos would help a lot, of both the original and replacement cylinders.

daryl bane · Aug 28, 2018

I haven't redone the photobucket thing, but very similar to an old Harley, or Indian or... V twin, two push rod tubes up the front. I have some low melting point metal, used to bend tubing, but I would think Plaster of Paris more ridgid.

Limy Sami · Aug 28, 2018

FYI.

I don't know about other LMP metals, but both lead and soft solder shrink on changing from liquid to solid, so will be loose.

thermite · Aug 28, 2018

daryl bane said:
I haven't redone the photobucket thing, but very similar to an old Harley, or Indian or... V twin, two push rod tubes up the front. I have some low melting point metal, used to bend tubing, but I would think Plaster of Paris more ridgid.

Cerrocast is one where shrinkage has been minimized. "Sweat" solders for plumbing may be "tuned" to EXPAND, rather than shrink, so as to insure strong, tight, joints.

You don't want the cost, heat, risk, nor even the mess of clean-up of ANY of those on sumthin the size and fragility of a finned "jug".

Plaster of Paris, rather. "Food grade" white vinegar is cheap enough.

Try it out on sumthin' else first.

Mud · Aug 28, 2018

daryl bane said:
I haven't redone the photobucket thing, but very similar to an old Harley, or Indian or... V twin, two push rod tubes up the front. I have some low melting point metal, used to bend tubing, but I would think Plaster of Paris more ridgid.

You can post photos directly here w/o an outside host. In fact that's preferrable. I've opened up pushrod tube clearance on aftermarket big bore barrels just by side milling into the fins, the endmill axis same as the pushrod axis, never had a fin break or sound like it was going to break. FWIW using a roughing endmill reduces pressure and prevents chatter if the right size is available.

thermite · Aug 28, 2018

Mud said:
opened up pushrod tube clearance on aftermarket big bore barrels just by side milling into the fins, the endmill axis same as the pushrod axis, never had a fin break or sound like it was going to break.

Old style CI, Nickel-alloyed, or Alfin, though?

daryl bane · Aug 28, 2018

This was my original idea, good to hear it can be done.....without breakage. I need to figure out to post photos, but you seem to know exactly what I am trying to do. I may utilize plaster of paris and or wood stoppers between the fins for peace of mind. Thanks all for the good ideas.

thermite · Aug 28, 2018

daryl bane said:
This was my original idea, good to hear it can be done.....without breakage. I need to figure out to post photos, but you seem to know exactly what I am trying to do. I may utilize plaster of paris and or wood stoppers between the fins for peace of mind. Thanks all for the good ideas.

Suggest the poly wedge paks sold for door-jamb adjusting, "Big Box", not wood. Wood swells when wet. Resist the urge to chip or thermal-shock the gypsum off. Fins may not be au fait with that. Vinegar and patience, rather.

daryl bane · Aug 28, 2018

Nobody has asked, but its a fun story to tell. I have owned this bike for 35+ years and traded labor on a very bad Jaguar XJ6 in trade for this bike, as I didn't have any money for this sort of thing. I didn't know what it was at the time, but that it "looked cool", and being a British bike enthusiast, had to have it. The fellow that owned it and the XJ6 was a would be "artist" and was going to make a coffee table out of it. True. It was very complete and original but restoration has been in fits and starts over the many years and just now picking up speed. A 1931 OHV 680 Brough Superior is what it is, not an SS100 mind you, but quite a nice find in Texas.

I am sure the knowledgeable just spit up on their keyboards but ....

9100 · Aug 28, 2018

Have you contacted the Antique Motorcycle Club of America? They might find a source of cylinders ready to go.

Bill

Turner_Whitworth · Aug 28, 2018

Ah, in that case you will want a Broughing endmill.

Finned cast iron cylinder machining question

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