Lapping and grinding a D2 die

epmtool · May 16, 2008

I am making small D2 die plates .150 thick with a .501 +.0002 -.0000 hole in the center. I believe this will be used to stamp out .050 thick plastic most likely with a .500 +.0000 -.0002 punch ( thats the clearance and tolerance our brilliant engineers always come up with )

My plan is to bore the holes undersize and make a lap to bring the hole to size.

1. How much material should I leave for lapping?
2. What size and material should I make the lap? (I am making 12 pc. will I need more than one ? )
3. Any recommendations on the spindle speed or "feed" techniques?
4. What grit lapping compound should I use?
5. Should I finish the hole lapping before finish grinding thickness?

I never lapped before so any input would be appreciated.

Holescreek · May 17, 2008

I think you left out a bit of useful information. What machine are you using to bore the holes? How good are the bearings? Shouldn't there be a 1.5 degree taper in the die relief? Do zero tolerance die clearances work on anything? :skep:

Assuming that you can bore the hole to within .0005" size for lapping, why not just finish it? :toetap:

-Mike

rj newbould · May 17, 2008

From the lack of details, the only thing I could give a firm answer for is that you should finish the hole before the final grind on top.

How much you leave for finish is partly dependent on the quality of finish you can bore. The better finish and roundness you can get, the less you need to lap. For a ream finish. .001 or even more. A good round bore finish as little as .0002/.0003. .0005 should be safe with a normal bore finish.

An adjustable brass lap works well with that size.. Buy it. Buy a holder and buy the barrels. Lap from the bottom of the plate so that any taper will go in the right direction. Don't pass the lap all the way thru to avoid bell mouthing the hole.

There is a wide variety of compounds from Clover coarse, medium, and fine all the way to diamond compound. All depends on what's available to you and the end result you need.

With that die thickness, and punching plastic, you will probably not need a relief taper.

Make some test pieces to practice on since this is new to you.

easymike299 · May 17, 2008

epmtool said:
I am making small D2 die plates .150 thick with a .501 +.0002 -.0000 hole in the center. I believe this will be used to stamp out .050 thick plastic most likely with a .500 +.0000 -.0002 punch ( thats the clearance and tolerance our brilliant engineers always come up with )

If the plastic is .005 instead of .050 the clearance might be correct.
If the plates lend themselves to stacking and fastening together, honing is the way to go. All twelve could be honed together.
Gene

rj newbould · May 17, 2008

Fine blanking dies operate with low clearances like that. I just don't know if fine blanking works with plastic.

Much depends on what kind of plastic and if it's filled.

epmtool · May 17, 2008

There are 4 10 -32 holes that I could use to bolt them together with 6-32s and hone them. I considered this in the first place but I saw our shift "expert" (who happens to be on vacation so I can't ask him) lapping them with a solid aluminum lap so I figured that would be the way to go.
I have honed before but nothing under 1.5 and nothing with .0002 tolerance ( not that we have a inspector that would check it)
Any thoughts?

easymike299 · May 17, 2008

Cold rolled would be better than aluminum.
Tool steel would be better yet.
Heat treated Rc 40-50 tool steel would be still better.
A series of progressively larger diameters is best.
Laps do not need to be dead soft. The harder they are the longer they last . They will cut just as good if not better. It's the abrasive between the lap and the workpiece that does the work, not the abrasive that gets imbedded into the lap.
Gene

chet · May 17, 2008

Edm?

12 pieces with how many holes? with the tolerance of .0002" sounds like EDM work to me.
-chet

rj newbould · May 17, 2008

easymike299 said:
Cold rolled would be better than aluminum.
Tool steel would be better yet.
Heat treated Rc 40-50 tool steel would be still better.
A series of progressively larger diameters is best.
Laps do not need to be dead soft. The harder they are the longer they last . They will cut just as good if not better. It's the abrasive between the lap and the workpiece that does the work, not the abrasive that gets imbedded into the lap.
Gene

IMHO...Solid, progressively larger laps can be very good. I do a lot like that myself. For 12 pieces, however, a series of laps is not economical. It is especially difficult for one who has no lapping experience. Ever had one sieze up in your part?

An adjustable barrel lap will do him well. It is hard to control sizes with a single split lap, and they will not correct a small out-of-round condition.

Bolting all the pieces together for lapping is tricky too. It's easy to get a barrel shape or bell mouth condition. Either one will give you variable sized parts, and it's not that easy to clean out the compound frequently to check sizes all the way through the stack.

Holescreek · May 17, 2008

Just curious. Why lap? Why not hone? Seems to me like holding a lap in a spindle of unknown runout would cause more harm than good. Why not bolt them all together with a pin in the die hole, push out the pin and hone all at once? :confused:

-Mike

rj newbould · May 17, 2008

Honing would be wonderful for these. My impression is that they don't have a hone or they would have wanted to do that in the first place.

How 'bout it epmtool?

BTW, I use solid progressive hones plated with CBN for my holes. Much better than lapping compound.

rj newbould · May 17, 2008

bryan_machine said:
Is there a pointer to some simple exposition about how honeing is different from lapping? (And they both differ from grinding in that there's a tool + compound rather than just an abrasive tool like a wheel, right?)

I don't know if there's an "official" difference..

My definition of honing is when you use an abrasive "stone" or the like, with just oil or water lubricant. Lapping uses a free abrasive between the part being lapped and the lapping tool.

eKretz · Jun 8, 2008

RJ, where do you get your CBN hones?

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