Could one of the members who are machinist's answer a basic question for me?
I was reading a thread at another group and see that there is at least one. (I am not) that also posts over here.(I have a FMA Co-Pilot to liquidate at some point, btw...)

http://www.rcgroups.com/forums/showthread.php?t=837543

I have an Echo cylinder with the fins turned off.
The OD T.I.R is within .0005” which is just peachy.
The trouble, is that I’ve managed to turn a taper of
About .0025” within a space of 1.570”.(mandrel to cyl.fit too loose)
The amount of stock I left to play with is only ~.010”
Maybe a tad more,What are my options…?

Nitro, I do not quite understand your problem. Can you please rephrase? the T.I.R. part, your mandrel fit , the stock to play with, and where the taper is?

I am trying to visualize what I would do, but I cannot quite follow your use of the lathe, and materials. Please do not use abbrevations. English is not my native language.

edit:
If I understand your post well:
I would use a mandrel with straight fit section and with a slight taper in the end, just enough to hold the cylinder tight. As emergency measure, a dab of hot melt could secure the cylinder to the mandrel, that should stay in the lathe, or be scrapped.

pe reivers
Thanks for you response.

T.I.R = Total indicated runout as was checked on the outside
diameter of the cylinder.

The mandrel is in the photo below.
The mandrel diameter was turned to allow one wrap or mylar tape
around the area where the inside of the cylinder fits for protection
I should have split the mandrel for adjustment.
The taper is on the "x" axis. (left to right as pictured.)
A four jaw chuck was used to hold and the job.

Ive only had my lathe for a while so im no ways near an expert,but i would try 2 things.
1--switch to a 3 jaw chuck and use inside jaws and clean up as best as possible.
2--go to a muffler shop,harbour freight,somwhere that sells cheap tools and get a tailpipe expander.Its a tool that looks like a mandrel with slices all around it and when hammered into a muffler tailpipe or thin walled pipe it makes it round again.This might work if a bolt could be installed through the middle and then the cylinder put on it and tightened down from the end with a washer to hold it snug.Then run it in lathe and clean up as best as posible.
If all fails,get another cylinder and make a better mandrel.What echo is that cylinder off of.

Hello,Buck
Thanks for the tips.Do you think that might distort the clylinder?
I sure don’t want to do the chrome bore any harm.
The engine is a 23.6 cc model.

Oh, and thank’s for the PM a while back concerning the feller out your
way in Williams. He fixed me right up!

I would put a piece of double stick tape on each of the jaws.Then install cylinder and check the runout.The tape should squeze the same amount.I would take small or fine cuts so it wouldnt take a lot of pressure.
If ya go the muffler expander i wouldnt worry about anything because its going to grip around the whole cylinder,and again take small or fine cuts.
Your also welcome for the PM.Ya might give him a call again.That man has enough experience in engines and shop equipment is as many years as ive been born.

that tail pipe expander is a good idea, I'll have to give that a try since I have one... for under $10 that's a pretty cheap lathe tool...

OK, I got your problem:
Runout concentricity to cylinder bore realy is not critical, but removing a slight amount of metal to get the fit to the cooling jacket just right is important.
Here is what I would do:
Fit the mandrel in the 4-jaw.
Make strips of newspaper-paper, about 1/2" wide, and paste these to the madrel with a bit of grease. This paper is 0.002" thick, and should do well to get the right friction fit between mandrel and cylinder.
When satisfied, tap the cylinder on all the way and adjust the runout with the 4-jaw. If you want to be very precise, also check runout on the mounting flange to be sure the cylinder bore is wobble-free. I do however not think that is critical, because the bore should be perpendicular to that mounting face if your cylinder is OK to start with. Whichever way you fit that cooling jacket will not change a thing to bore-flange alignment.
On each check station, also check lengthwise integrity (straightness), so you will have no wobble. Tap- and adjust the mandrel in the jaws until you are satisfied with straightness and runout of the cylinder. When done, you should be within 0.002 T.I.R on all possible sections.
I did a similar thing in a 3-jaw. It took me quite a while. A 4-jaw is much easier to adjust.

The cooling jacket need not be a press fit. A smooth tight slide fit will do (thump pressure fit). The cylinder in operation heats up and expands right onto the cooling surface, as is the case in our glow engines.

Ill be heading to the valley this weekend maybe so im going to check harbour frieght and see what they have.I just turned the fins down round on my lathe.I just stuck the base flange as straight as i could in my 3 jaw and took light cuts.It turned out really nice.The tailpipe expander would be great id think.Im in the process of making a mandrel for cylinders,ill have to put a pic to show what im doing.

“…Runout concentricity to cylinder bore realy is not critical, but removing a slight amount of metal to get the fit to the cooling jacket just right is important.
Here is what I would do: …”

pe reivers

Exactly. English is my primary language, I could not have said it as well!

I found that by trying not to cut the mandrel length (to save the stock for another use) That the runout was being exaggerated... I cut it in half, and will split the end next to the drive dog for a small wedge to hold the cylinder snug,but not heavily forced to the mandrel.

I read up on the theory of external lapps and made one. I made it .001" undersize before splitting and segmenting.
I gave it a test on the part,but I probably should take care of most of the.0025 taper first.
The little can in the picture holds two grits of lapping compound.


Buck: Whatcha building there?

I missed a couple words in my last post until i just read it.I took the stock cylinder off the ryobi and turned it down so its round so it looks more like an airplane engine.The last time i ran a lathe was in high school so im just starting to play around with this.Ive made some 6 bolt prop hubs,single hubs,timing sensors out of flywheel centers,ect...Im finding more uses evryday.For instance,my son needed a heli coil for his aluminum eldebrock intake manifold.Well,ya have to buy the kit.I have drills and taps,i didnt need the kit.heres what i did:
Drill out existing hole for 7/16 tap
tap 7/16ths course thread.
chuck 7/16ths all thread in lathe
drill out center,tap for 3/8ths course thread
cut off 1/2 - 5/8s inch
install in manifold with a little locktite.
my Cost==25cc maybe------------helicoil kit=$17.00----$22.00-plus,what do ya do with the leftover helicoil parts?
I also have a little twin project im trying but its not going real fast.

Nice one Buck. I have many years experience and I don't know that I would have thought of that one... But now I know!

AV8TOR

Ill tell ya,i went to the checker and they dont sell a helicoil.You have to buy the whole kit.Man have things changed since i was turning wrenches.[fulltime].Used the lathe again,idle screw for my other sons racing 2 stroke honda.somehow the throttle slide was sticking.Removed screw,the one that rides in groove on side carb, in slide,chucked in lathe,yup,out of round.Tapped with hammer 1/2 dozen times,little here,little there,nice and straight and throttle works perfect.Cost====FREE!.

lathes have all sorts of nice uses, that is until the part you're working on slips in the chuck (because you were being lazy and didn't use the center) and you break a main drive gear tooth... luckily it's just a 7x12 and little machine shop has them for cheap , but this also means I have to dissassemble the head stock and wait for shipping... not looking forward to that part

The taper problem turned out to be a substantial twist in the 36” bed on my
old Atlas lathe. The cabinet/bench was not stout enough to resist any attempt
At counter twisting with shims,so I made up a stout top from “c” channel
Notched and welded it in place. Leveled it in, and the twist came right out.

Just something to check if your lathe is turning an unwanted taper.