Machining (3MM ±.002MM) 50mm length Bore

behnod · Dec 25, 2018

Hi everyone .

I'm afraid is possible to make around part with a 3mm hole in the center which has ±.002MM tolerance in diameter . Please let me know the normal procedure of this kind of parts and also the cheapest and fastest way as well. the repeatability of the procedure is very important .

Best Regards And Happy Christmas

MattiJ · Dec 25, 2018

Out of my league but how about gun drilling or EDM folloved by lapping.
Not cheap nor fast.

athack · Dec 25, 2018

The best way is internal lapping. Like MattiJ said, gundrill would be a good way to start then lap. You can drill then ream then lap also. Search internal laps to find a vender for the tools.

Limy Sami · Dec 25, 2018

Are you sure the decimal point is in the right place? ………………… 0.002mm is 0.0000787''

DDoug · Dec 25, 2018

Needs parts RIGHT NOW !

Material ?
Part size ?
Machines available ?
Quantity needed ? Per month ?

Budget ?

magneticanomaly · Dec 25, 2018

Disclosing your application would get you more and better answers

FredC · Dec 25, 2018

I have gotten diamond laps from these people:
dicoat.com
Still using them today, got the last one 8 years ago. Cost about $250.00 back then for 3.5mm. if they can do 3mm it will probably be part of your solution.

RODELU · Dec 25, 2018

How would you measure your I.D. +/- 0.002mm? Agree with Limy Sami, you decimal point is probably in the wrong place.

HuFlungDung · Dec 25, 2018

Limy Sami said:
Are you sure the decimal point is in the right place? ………………… 0.002mm is 0.0000787''

The ass is a very sensitive gauge. You can measure very precisely when you pull something out of it.

behnod · Dec 25, 2018

Thank you very very much for all the answers .
Yes that's right. the decimal is exactly in the right position .the tolerance is just 4 thousands of a millimeter . Material is 1.7225/42CrMo4. the quantity of parts is 500 pcs .i'm thinking of air probe for measuring the diameter( please let me know if you know better way for measuring).
Actually i was thinking of drilling to 2.95 then burnishing or completely doing using wire cut machine.
I have never done internal lapping before but i'll certainly consider the process .any other helps would be really appreciated .

Limy Sami · Dec 25, 2018

MMMMMMMMMMMMM? Unless I REALLY REALLY knew what I was doing (which I DON'T!) , I wouldn't walk away from that job, I'd run.

michiganbuck · Dec 25, 2018

Seems a Sunnen hone could do that , knew a fellow who had +- or just + .0002 on thousands of small parts.

.002mm almost one tenthousandths. That is liken to a mile in grinding...But a bore can be tougher that grinding ..sometimes.

Good rifle barrel might be .0005 for 20 inches long or so...

Agree I dont know if sunnen hone goes that small
https://www.sunnen.com/graphics/assets/documents/19ffb93a1003.pdf

Small bores:
https://www.sunnen.com/graphics/assets/documents/18e18e733d7b.pdf

Re sunnen:
POWER STROKING SMALL BORES
Most bores in the .060-.3125 in. (1,5-8,0 mm)
diameter range can be power stroked. In many
cases, power stroking does an even better job than
manual because the stroke length is consistently
correct, preventing the shearing of these small
stones by improper stroking

Dan from Oakland · Dec 25, 2018

Have a really in depth conversation with your customer so you can understand his part function and his need for that tolerance. Then ask him if he understands that temperature is going to ruin his day unless that is controlled as well. You say nothing of the positional tolerance for the feature other than "center". If ya get the decimal point moved over one place, then honing may be a reasonable finishing method. No way you're going to wire edm to that tolerance.

triumph406 · Dec 25, 2018

Presumably it has to straight within that tolerance as well?

If your hole is not straight to begin with, a hone or diamond lap isn't going to fix an 'out of straight' condition due to the diameter and length. The hone or lap will not be stiff enough to fix that condition.

Good luck!!

litlerob1 · Dec 25, 2018

17x diameter isn't too insane. Straightness is going to be more challenging, than diameter. I'd Drill to see if you can keep it straight.

Part in the Main Spindle on a Lathe with Live Drilling would be ideal.

R

gappmast · Dec 25, 2018

A Sunnen hone can do the part. A standard length mandrel will be a little to short and the part will have to be honed from both ends. Sunnen can make an extended length shank to hone it all from one end. Question I have is what is the material, hardness and part weight. Is there any call out on bow? While the hone can hold the size from end to end on this configuration it can not straighten a hole with bow.

The part is hone able but not a slam dunk by any operator so bit it accordingly.

MattiJ · Dec 25, 2018

litlerob1 said:
17x diameter isn't too insane. Straightness is going to be more challenging, than diameter. I'd Drill to see if you can keep it straight.

Part in the Main Spindle on a Lathe with Live Drilling would be ideal.

R

Look on few gun drilling companies reveals that exit location could be the hardest part(if there is requirements)
0,0005 in/inch seems to be archievable centerline drift for contra-rotating gun drilling and hole straightness appears to be sbout one tenth of that. For 50mm depth 20um centerline drift and 2um hole straightness if your lucky.

Booze Daily · Dec 25, 2018

HuFlungDung said:
The ass is a very sensitive gauge. You can measure very precisely when you pull something out of it.

That’s where most of my quotes come from.

litlerob1 · Dec 25, 2018

MattiJ said:
Look on few gun drilling companies reveals that exit location could be the hardest part(if there is requirements)
0,0005 in/inch seems to be archievable centerline drift for contra-rotating gun drilling and hole straightness appears to be sbout one tenth of that. For 50mm depth 20um centerline drift and 2um hole straightness if your lucky.

I agree with you. So the center line drift could (not-ideally) be corrected with a second operation, turning/grinding between centers. But 2 micron Straightness is obviously going to be a problem.

Like I said, I would at least try Drilling in as near to perfect conditions as possible, and see where the part ends up. Go from there.

R

gmc1724 · Dec 26, 2018

camscan said:
Cheap,fast and repeatable,and I thought you might have a problem. The first two maybe but the third one is definitely out the window.

Sounds like someone's F××ked-up on the quote to me, if he's on here asking can it be done then he probably didn't see it on the drawing when he took a shot at the quote. Unless it's his no.1 customer I'd be politely handing it back, if it is his no.1 customer than he better find someone capable of doing the parts and take it on the chin.

Machining (3MM ±.002MM) 50mm length Bore

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