Educate me on brass barrel laps please

[Brian Rupnow]

I am about to lap the 1" bore cast iron cylinder on the i.c. engine I am currently building. On the previous 7 i.c. engines I have built, I turned a piece of round aluminum to .002" to .003" less than the cylinder bore, coated it with 300, then 400 then 600 grit carborundum paste, and lapped by hand with a turning/sliding motion. Then I finished up in the lathe by holding the round aluminum in the chuck, holding the cylinder in my hand, and running the lathe on its lowest (115 rpm) speed while moving the cylinder back and forth about 1" for about a minute. (This is very scary!!)--Now maybe I'm ready to move things up a notch. Travers Tools has "brass barrel laps" for about $30--see attached link. The literature in the link says that these laps are adjustable up to 15% of their nominal value. I have never used one, and I don't know anyone who has. Does the lapping process wear these brass laps out? Are they a worthwhile purchase? I would like to hear from someone who has used this type of lap, and what you think of them.---Please----Brian
http://traverscanada.com/skulist.asp?RequestData=CA_Search&navPath=All+Products%2F%2F%2F%2FUserSearch1%3Dlap&q=block+id+112470+and+class+level3+id+29980&minPrice=$3.23

 

[Hrcoleman66]

In a previous life I worked for a cold forging company. Most of the tooling was Tungsten Carbide that was turned/ground and then lapped to finish.

The majority of the lapping was done with brass and copper lapps.

Basically, the lapp was turned to just under the diameter of the bore to be lapped and a slot was cut down the middle for the entire length of the lap with a hack saw.

A small wedge was then placed in this slot which was used to adjust the size of the lapp during the process.

Yes, the laps did wear. They went through an awful lot of copper and brass.

You might be better off to turn your own lapps from scrap brass.

Cheers,

Hugh

 

[kf2qd]

You can make a lap out of steel also. No need to buy something to do the job. it is not like you are going into production on these cylinders. I have made a lap using a piece of CRS, coated it with valve lapping compound and using it to final size a small castiron cylinder. Came out straight & smooth.

No need for something fancy.

 

[gbritnell]

Brian,
Yes the laps wear out but you get quite a bit of use from them. I use them all the time. Don't forget you're only taking off .0005-.0015 of material (per side). Like almost anything else they can be made in the home shop but I think it's more a matter of convenience to purchase them. Once you have the threaded rod then the lap head can be replaced if and when it wears.
gbritnell

 

[Tom Jamboretz]

Phillip Duclos describes the operation you are speaking of in his "Odds and Ends " engine plans. I have used it and it is quite simple and gives great results. Well worth the read. TJ

 

[Brian Rupnow]

Tom--I have that book, and I built that engine, but I don't remember anything about laps in the article.---But then again, I'm 68 and don't remember things quite as well as I once did. I will go upstairs now and look in the book. Thanks for the heads up.---Brian

 

[Brian Rupnow]

Okay--I'm not as old and senile as I thought. I believed Tom was telling me that Philip Duclos described brass laps in his article. He doesn't. He describes the method I currently use. that is where I learned ho to do it in the first place.