Lapping compound

[joeby]

Dave and Paula,

I will agree that the lap used can be made of material at hand with good results IF a lapping compound is used that is correct for the job.

I re-read my post (glanced actually) to see if I posted erroneous information; but I don't think I did. Unclear information, probably! In the second paragraph, I mentioned different types of lapping compound, some won't break down easily and will embed into the work, diamond being nasty for this. A softer lap helps prevent grit remaining in your workpiece.

I base much of this on what I've learned on molds and dies over the years, not on small engine building. I can say from experience that I've too many times seen someone lap a hole in a mold with a hardened pin and diamond paste. No matter how well that hole was cleaned, it would leave black marks on the molded part. This was the lapping compound still doing it's job!

Brian,

No, not stupid at all, just one of those things that you pick up as you go. I'm sure somewhere along the line, books were written on the subject of lapping, and I may just have one somewhere; but it sounds like you were given "run in" instructions perhaps?

Just my $.02.

Kevin

 

[malcolmt]

Jeez----After seeing all the posts on this subject, I don't know how I could have got it so wrong!!! I'm pretty sure that the advice I gave on putting toothpaste on the piston and working it in and out of the cylinder by hand was given to me by someone on this forum, way back a year ago when I started making my first steam engine. So---No friggin wonder I never had much success with it. Ah well, colour me stupid. : :

Brian.

There are no stupid people on this forum.

There may be members who haven't yet read the post required to point them in the direction they need to go !!!

Kind regards

Malcolm

 

[rleete]

Brian, I heard the 'use toothpaste to run in' thing too. Maybe read it here, or on a similar forum?

Your only confusion is that occurs after lapping if you need that last little bit to make it smoother? Dunno. You're the one with the running engines, so you must be doing something right. More than one way to get to the end result, too.

 

[Philjoe5]

Brian,
I'll bet I've seen the toothpaste reference to lapping a half dozen times. One I'm sure of was in one of the model engine magazines....I haven't actually used toothpaste but in principle I did the same thing..add some abrasive paste to a cylinder and work the piston back and forth. Ever since reading some posts on this forum several months ago on the subject, I don't lap that way anymore. I guess this is part of the educational process :

Cheers,
Phil

 

[Brian Rupnow]

Me Stupid??? No way!!! Misinformed---Well, yeah ;D ;D. But whoever told me that method in the first place did it with absolute sincerity, and I'm sure they believed it themself. No harm done---And I did point out in a much earlier post that I hadn't had spectacular results using that method.

 

[rake60]

I am a firm believer in using toothpaste for the final run in.
I also use it as a lapping compound.
I find the industrial compounds too aggressive for my touch
with a lap.

Rick

 

[Philjoe5]

Rick,
I use Nonox, a metal polish, as a lapping medium. Since I use a gel toothpaste , that's out for me. :'( But am I right in saying any lapping medium you use shouldn't be applied to the mating parts? There seem to be some pretty good arguments against doing that.

Cheers,
Phil

 

[rake60]

Rick,
I use Nonox, a metal polish, as a lapping medium. Since I use a gel toothpaste , that's out for me. :'( But am I right in saying any lapping medium you use shouldn't be applied to the mating parts? There seem to be some pretty good arguments against doing that.

Cheers,
Phil

Rof}
Yes gels don't work and engine cylinders are not concerned about fresh breath or cavity protection.
I do also use auto paint polishing compound for steel parts.
I realize that a tin of that costs 1/10 of the same amount of clover compound, so it can't work as well.
I'll keep that my personal secrete.

Rick

 

[dwentz]

There is nothing wrong with using a little lapping compound (Toothpaste) to lap in the piston to the cylinder. I hand lap parts together all the time. The key to to clean them up, and to keep the lapping to a minimum. When I build the racing kart engines, I have lapped the rod to the crank a few times, and it has always worked well as long as I get all the lapping compound back out. You just need to be sure to use a lapping compound that will not imbed it self into the metal. My copper laps are next to impossible to get all the lapping compound out. In fact if you use different grades you need to change the lap when you change grades. Something to keep in mind.

Dale