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RacinNdrummin
05-30-2012, 01:23 PM
I have a question that maybe the great minds here could help me out on. I have to hone a .400" bore to a super fine finish, the bore appears to be hardened (I had an EDM shop cut the bore) . There is a tool steel plunger (That will be made to fit the finished bore) that rides in the bore, with no seals, its sealed by the diesel fuel its pumping, and the plunger to bore clearance is about a tenth of a thou. The seal is important, but the finish is even more important, or the plunger will seize in the bore. I dont see honing to tolerance being a problem, but I dont know of the best way to get a super fine finish.

My question is, is there any way a HSM'r could get a micro finish on something like this, and if so, what do you think would be the best way of doing it. Time is not an issue here, this isnt a paying job... Yet anyway.

Appreciate the the help.

Justin

RWO
05-30-2012, 02:35 PM
600 grit is about the finest hone abrasive I have seen. To get finer you will likely need a expanding brass lap charged with diamond grit in the 1200 to 6000 grit range.

MSC is one supplier that sells the laps and the abrasive compounds. They are not very expensive. It will be difficult to keep the hole diameter uniform within .0001 because the lap suface will likely be shorter than the bore length. Therefore the lap will have to be stroked up and down the bore leading to multiple possiblities, all bad.

I suggest you practice your technique on a dummy workpiece untill you get the hang of it.

RWO

Ian B
05-30-2012, 03:26 PM
How about roller burnishing? Haven't tried it, but I believe it gives a high finish. You might be able to find a suitable size on Ebay etc.

Ian

rklopp
05-30-2012, 04:38 PM
I've been lapping my Nano 0.1-cc engine cylinders with 3-micron diamond on a commercial brass lap. It cuts slowly, but leaves practically a mirror finish.

Rustybolt
05-30-2012, 05:39 PM
How about roller burnishing? Haven't tried it, but I believe it gives a high finish. You might be able to find a suitable size on Ebay etc.

Ian


I was going to suggest that. The balls are pretty expensive if you're just doing one part.

Are you using a Sunnen hone?
Sunnen has a a lot of finishing solutions including cork "stones" that you charge with lapping compound.

Ian B
05-30-2012, 06:56 PM
Rusty,

Ball? Ah - I found that. you're thinking of pressing a hardened ball axially through the bore. That'll work.

What I had in mind were these things: http://www.elliott-tool.com/id-roller-burnishing-tools/

Sort of an expandable needle roller bearing. They have ahardened, tapered internal needle that you push further into th etool, pushing the rollers out a tiny amount, until the desired bore is achieved.

Ian

Mcgyver
05-30-2012, 07:57 PM
just keep lapping with progressively finer pastes. I have no way to measure the finish, but it starts to become reflective at 1000 grit, if not enough keep going. Technically you need a different lap for each gri, make a batch of expanding ones and have at it

tlfamm
05-30-2012, 08:40 PM
Clover (LOCTITE) offers silicon carbide lapping & grinding compounds to 1200 grit:

http://www.use-enco.com/CGI/INPDFF?PMPAGE=265&PARTPG=INLMK3&PMITEM=619-0178

CCWKen
05-30-2012, 10:17 PM
I don't have a picture but I have a set of small bore hones. They are basically a rod with opposing spring steel leaves attached lengthwise. I use lapping compounds. (Powdered that you mix with light oil.)

elf
05-30-2012, 10:54 PM
just keep lapping with progressively finer pastes. I have no way to measure the finish, but it starts to become reflective at 1000 grit, if not enough keep going. Technically you need a different lap for each gri, make a batch of expanding ones and have at it

Diamond lapping compounds are available down to 200,000 grit. The finest grits are usually sprayed on the lap and the lap is usually quite hard. Larger grits (smaller number) are used with a softer lap and the diamonds are pressed into the surface. Here's one supplier: http://www.amlap.com/alw/page18.html

Note: I have not ordered anything from this company, so I can't vouch for their reliability.

RacinNdrummin
05-31-2012, 01:08 AM
Thanks guys, Shortly after I posted I found a source for diamond lapping compound and I was brainstorming on some ideas on how to get it done, some of what i was thinking was similar to you guys have said here. That may be the way to go about it fortunately I have a spare part to compare surface finish, so as long as I can acheive a similar finish, it should be good enough.

I am interested in the ball method though, just curious if something like that could be used effectively on a setup like this, what is the process for soemthing like that?...

RacinNdrummin
05-31-2012, 01:13 AM
Ian, that roller burnishing setup is VERY interesting, I think I might request some info on that.

Hopefully the setup isnt as expensive as it looks.

madman
05-31-2012, 07:09 AM
Sounds like the way to go economically, We used all types of Diamond Paste to hand polish die steels, a slow tedious Job, made me wish I still smoked Ganja while doing thae polishing Jobs some nights in the Die Shop.

macona
05-31-2012, 08:22 AM
Diamond can become embedded and never leave. You might look at something like Timesaver Lapping compound

http://www.ws2coating.com/timesaver.html

rkepler
05-31-2012, 11:06 AM
Note that you'll want to remove the HAZ in the work left by the EDM. Not knowing the process that you had done I couldn't guess the depth of the HAZ. If the bore diameter change is great enough in the lapping/honing process it'll have been removed when you're finished but you might want to keep it in mind if you're looking at ballizing or rolling the bore.

Like Macona I also use Timesavers for some lapping, but with the finish you want you'll have to go to a very fine lapping compound after the finest Timesavers. I've had good luck embedding lapping compound in through hole laps (spread lapping compound mixed with very light oil on hardened plate and roll the lap across the plate using another hardened plate above). In your case you'll need a few of the lap bodies turned to a close match - the 13/32 FlexoLap at .406 would be a good start if your existing bore is down around .395. After charging the lap wash it off in kerosene or thinner to get the excess lapping compound off else it'll embed in the bore.

When lapping you will have a tendency to overlap on the ends and underlap in the middle, with care this can be minimized. But the easiest solution is to place plates on both sides of the bore to take up the bell-mouthing. The plates don't have to be the same as the bore material but it helps with the lap feel.

The feel in the bore when lapping is something you have to pay attention to - too little drag and nothing is happening, too much and the lap will expand with heat and lock up. You have to play with it a while to get a feel for it. Lucky for you a small bore is easier, lapping a 1.375 bore can about break your wrist if it locks. I prefer to lap in the lathe if I have to hold the work but the mill would be better for this work - no feel (might have to go by sound) but less bell-mouthing.

The FlexoLap barrel laps are available from a lot of folks, I've even ordered them from the maker at http://na.dmecompany.com/ You will need one barrel fro each size in lapping. In lapping you have to work out the scratches from the previous lap before moving to the next, it's a lot like sanding - skipping one lap size means about 4x more lapping in the next. Don't be tempted to turn down a lap ato change the lapping compound, some always remains and you're making the lap a lot less parallel in the bore and slower.

Good luck. You might mention the EDM process used and the material and someone might figure out how thick the heat affected zone will be. If the base materal was heat treated you'll want to take it all out to get to the original base material.

TGTool
05-31-2012, 11:54 AM
If the part is hardened as mentioned in the initial post I would think ballizing and roller burnished would be out. They both depend or re-forming and work hardening the surface which won't work NEARLY as well in hardened steel. Still, they're processes worth knowing about.

Rustybolt
05-31-2012, 12:09 PM
Thanks guys, Shortly after I posted I found a source for diamond lapping compound and I was brainstorming on some ideas on how to get it done, some of what i was thinking was similar to you guys have said here. That may be the way to go about it fortunately I have a spare part to compare surface finish, so as long as I can acheive a similar finish, it should be good enough.

I am interested in the ball method though, just curious if something like that could be used effectively on a setup like this, what is the process for soemthing like that?...


I used an arbor press and a short brass rod with a smaller diameter than the ball.