making a barrel lap

[jdwardus]

hello every one. this is my first post on here.thou i belive i have read every post on here.anyways im building bollareo 18 all is coming along well.im needing to make a barrel lap is there any good plans for one iv read alot about them . but cant realy find good info on how they are made im looking to make exspanding lap

 

[MachineTom]

Well they are fairly inexpensive to buy, like $20 for a .750 size. To make one you need to be able to cut a fairly small inside taper in the slotted brass cylinder, then a matching taper on a expension bolt. Here's an 1.250 to look at, the .5 I have is the same just smaller.

 

[Mainer]

I've made one, more or less following that design. Having proved I can do it, I buy them. As Tom says, they are pretty cheap. One can hardly buy the material for the cost to buy one ready-made.

If you do make one, the real key is figuring out how to expand the barrel in the center.

 

[mu38&Bg#]

This method is pretty common for model engine cylinders.

http://modelenginenews.org/techniques/cylhone.html I used one the other day, but not for a cylinder.

Greg

 

[Swede]

I like these style of lap, and have had good success with them. I think they are easier and more forgiving than trying to modify a cheap brake cylinder hone. With practice and good measurement, you can control a bore to within 0.0002" or so, and also if you have a very slight taper, you can correct it if you want to, although standard practice for IC engines is to have a very slight taper with the narrow end of the cylinder at the head, and the wider portion next to the crankcase. That way, thermal expansion will create a more cylindrical bore, as the head end gets hotter than the crankcase end.

 

[mu38&Bg#]

Swede are you referring to the Arco or home made types?

While we are talking laps... I have only used a few so far. One Arco (brass) and a couple home made 6061 AL. Both times I charged with Clover 220 between ground steel plates. The grit didn't stay in the lap and soon the lap was not cutting. Is this due too much pressure? The bore in an aluminum part turn out so, so, but somewhat expected with 220 grit. While a 304SS part looked very nice deed.

 

[Swede]

If the Arco is the brass one in the picture, that's the one I've used and liked. How are you charging your lap? I'll admit that there is nothing fast about lapping, which is probably why I like them! If things go south, they do so slowly, and there is time to cease and make it better.

 

[Sshire]

Since I don't have unlimited time in the shop, I have to balance making a tool vs buying one.
IMHO the Acro (made in USA) laps are inexpensive enough that I'd rather buy them.

http://www.acrolaps.com/index.htm

Best
Stan

 

[mu38&Bg#]

Oops Acro. I think I made the small aluminum lap in the same time it took to gather enough items to make an order at McMaster worth the shipping. Acro are cheap though, and once you have the mandrel the brass laps are even cheaper.

I spread the Clover compound on the lap and roll it between ground steel plates with as much pressure as the 140Lbs of me can put on it. Maybe the 220 grit is too large imbed well in brass or aluminum? Next project will require 600 and maybe 1000 grit so I guess I'll find out.

Greg

 

[Swede]

I charged my laps by chucking them in a drill press, gobbing the clover onto a hardened steel flat, and pressing that hard into the lap barrel while its spinning slowly. I know in theory this alone should cut, but I cheat and add a bit of loose compound into the lap grooves, and thin it all with kerosene or WD-40.

I think the trick is in how the lap is expanded. I turn the drill press on dead slow with the cylinder on the lap, then try to stop the cylinder by hand while "pumping" it vertically. If it feels too loose, I'll expand the lap, and do so until there's significant drag. About 30 seconds or so later, the drag slowly vanishes as the cut takes place. Stop the press, remove the cylinder, add a bit more compound, reverse the cylinder back onto the lap, and expand it a bit more. The bored finish is slowly replaced by the frosted lap finish.

If you've got a number of cylinders to do, one of those expensive 3-point bore mikes is an awesomely useful tool to beg, borrow, or steal.

 

[modelman1838]

Hi
I needed to make a lap for a 1 1/2" bore cylinder for my rider-ericsson hot air engine which opened up more or less parallel. For the expanding part I used a No 2 Morse taper blank that was tapped 3/8 whit. I then made a sleeve which I bored No 2 Morse about 1.3"dia and slit this 6 ways from both ends like a collet. I Then made a further sleeve to fit over the 1.2"dia and to fit the bore. In this I made a single lengthway slit and loosely held in place with 2 grub screws. I found this lap opened up perfectly parallel and produced a very satisfactory bore in about 1 1/2 hours.
I always wet lap, that is to mix a little lapping power with a quantity of honing oil and then just brush onto the lap which I find easier than loading the lap with dry powder. The finish is slightly different.

 

[prof65]

Hi modelman

your way to make a barrel lap sounds very interesting... any chance to see a pic or a drawing?

Roberto