Lapping Aluminum?

[mu38&Bg#]

Has anyone out there had any luck lapping aluminum with a brass lap? I'm about to try and Acro brass lap in 6061-T6, but am unsure if I'll end up with Clover in the aluminum bore. I need to remove a taper from a 1.5" through hole 5.5" deep. I set up my lathe to cut the OD without a taper but the ID had about .001-.002" taper.

Greg

 

[Dan Rowe]

Greg,
I have used Clover lapping paste on aluminum and had no issues with the process. It was flat lapping on a ground steel plate but that should not make any difference.

Dan

 

[GailInNM]

Greg,
You should be OK if you keep the lapping pressure slightly on the light side and scrub the bore after lapping like you would not believe. Dishwashing detergent and the stiffest tube brush you can find. A baby bottle brush might work. As the saying goes "rinse and repeat" a couple of times. Actually this holds for any material, not just aluminum.
Gail in NM

 

[mu38&Bg#]

Thanks guys. The Machinists Handbook (which I usually consult) suggested that if the lap is not somewhat softer than the part the compound will end up transferred to the part. I don't really want to have to make a lead lap.

I'll give it a try. 220 Clover OK? I don't need a smooth finish, and I don't want to lap all day.

 

[Maryak]

I don't really want to have to make a lead lap.

Perhaps a hard wood lap ??? Easier and much cheaper than lead.

Hope this helps

Best Regards
Bob

 

[GailInNM]

Good point and excellent idea, Bob.
I used to use hardwood laps with excellent results and it would avoid any possibility of embedding of abrasive. Still scrub however. They were so easy to make that I would make up several for roughing, intermediate and finishing grits.

Turn hardwood to slip fit in bore and drill long hole to take a tapered wood screw.
Split with saw lengthwise a couple of inches.
Use tapered wood screw to adjust.

Gail in NM

 

[drookit]

used clover compound for many years , until I started repairing musical instruments, I was directed to "non embedding " lapping compound which is of a different grain structure that is less likely to embed itself in softer metals. This is most desirable in soft metal instrument valves ,and would likely be welcome in model engines built of softer metals.

 

[doc1955]

Good point and excellent idea, Bob.
I used to use hardwood laps with excellent results and it would avoid any possibility of embedding of abrasive. Still scrub however. They were so easy to make that I would make up several for roughing, intermediate and finishing grits.

Turn hardwood to slip fit in bore and drill long hole to take a tapered wood screw.
Split with saw lengthwise a couple of inches.
Use tapered wood screw to adjust.

Gail in NM

Hey that's the technique I have used in the past! I use old broom handles for small bores with great success. I usually turn down the dia about a half inch up the and only leave a half inch area at size on the end. That helps not create a taper in the bore.
I do use clover lapping compound on harder materials also have used just common auto rubbing compound and that also works good but anytime you use lapping compound or and grit you need to scrub the heck out of it plus use the hottest water you can as the heat helps any compound that may have embedded itself to release with the expansion factor.

 

[DLM]

I made a small hyd. valve i used 1/2 in. drill rod for the spool and the valve body was aluminum, i used 500 grit clover and the brass lap, it worked real well, got a real good fit.

Don

 

[jpaul]

Greg,
I lapped a brass cylinder using a mandrel made from plastic pipe. It worked very well for me and it may work well in your case. However I was only lapping tenths.

I have been told, like Gail suggests. your lap should be of a material softer than the part to be lapped so plastic or hard wood would be my material of choice.

Sounds like you have an interesting project. Do you need a constant diameter and/or polished bore? What grit would one reccomend to remove .002"?

 

[mu38&Bg#]

I ended up buying an Acro Lap. It was the biggest size they offered. This is a paying job so $30 was worth it. I tried it out using 220 Clover. I ended up with a bore that was ±.0002". It could be better. I can't check straightness, but it should be good. The 220 is probably too coarse, but seems OK to me. I did lose some lapping compound from the mandrel. There were bare spots. It turns out that my part probably didn't have as much taper as I thought. After I parted it from the chucking stock I found a ridge at the bottom of the bore. I'm not sure if I didn't finish boring or chips pushed the tool away from the part. Only the extreme ends of the bore needed much material removed. One part is done and I'll be working on the second one.

Thanks for the suggestions. This thread will go into my machining notes.