PDA

View Full Version : How would you finish bore this I.D.?



Hot Bob
02-01-2010, 11:30 AM
I'm wondering if anyone has any ideas that I haven't thought of on this. I use a Nardini MS1440 lathe. I need a way to quickly bore a finished I.D. of 2" in 2.25" x .250" wall DOM. The depth will be approximately .750".

I currently perform a similar operation on a different part (1.3125" bore) by rough boring it to 1.300" using a boring bar, then run a shell reamer through using my tailstock. I would do this operation the same way but a 2" shell reamer arbor uses a 4MT and my tailstock is a 3MT. I know I could use a reducer adapter but that gets kind of clunky.

Would it be possible to do this operation using a shell end mill on a 3MT arbor in the tailstock? If I can't do the bore quickly and accurately then the part will not be cost effective for me to produce.

Bob

Carld
02-01-2010, 11:50 AM
Are you really getting as good or better finish using the shell reamer?

What about making a holder for the 2" shell reamer or an adapter that you can use on your current #3 MT holder?

MrSleepy
02-01-2010, 12:01 PM
Dihart cutters are also a great way to get an accurate finished bore..
ALthough they say they are for ally...the ones I have cut brass and mild steel with no problems..

Rob

Hot Bob
02-01-2010, 12:12 PM
[QUOTE=Carld]Are you really getting as good or better finish using the shell reamer?[QUOTE]

I do not get as good of finish with the reamer as the boring bar produces. What I do get is accuracy with very little time investment. These are small production runs of 10-20 parts. Each end gets bored so that's 20-40 finished I.D.s. My current workflow on the smaller part is to face the part, run a single .060" cut with a boring bar, ream to final I.D., chamfer I.D., debur O.D., flip, measure part length, and repeat. I can knock out about four an hour doing it this way. I already know that I'll have to take two cuts with the boring bar on the larger part so time starts to add up. I can hold good tolerances with a boring bar but, that takes time.

Bob

Ian B
02-01-2010, 12:19 PM
Bob,

Can you hold a 2" shell reamer in your toolpost? If you can buy or make a floating holder, it'll make alignment less of an issue.

Ian

Carld
02-01-2010, 12:55 PM
Bob, I figured that was why you used the shell reamer but just checking.

The second part of my question was, can you make an adapter to fit the current holder and put the 2" shell reamer on? If there is some way to make a sleeve spacer and still have the dogs lock into the shell reamer it may work or you could machine dogs 90 deg from the other dogs and still use the 2" shell reamer.

What about turning down a #4 to a #3 taper?

Toolguy
02-01-2010, 01:04 PM
I would go for turning the #4 down to a #3 as mentioned above. Yes you can use a shell mill, but milling cutters always make an oversized hole compared to the actual tool diameter. The amount of oversize is not usually something to be relied on.

sconisbee
02-01-2010, 01:25 PM
Ideal sounding part for a turret lathe, but I would make up my own MT3 arbor for the shell reamer or turn down down the MT4 to MT3 if it wasnt too hard.

digger_doug
02-01-2010, 01:28 PM
Bob,
What is the tolerance your trying to hold ?

If the boring tool is making a good finish, could you
just come up with a way to set that final cut accurately ?

You have tried a minmag (base) and a 1" dial indicator
on the cross slide ?

Totally dispense with the tailstock operation, would shorten the
time somewhat, I would think.

EVguru
02-01-2010, 02:28 PM
I might think about using a boring head in the tailstock and set to the finish size.

Bruce Griffing
02-01-2010, 02:45 PM
+1 on the boring head in the tailstock. I would do that for sure because I have an MT3 boring head.

digger_doug
02-01-2010, 02:46 PM
How are you going to feed a boring head mounted in the tailstock ?

Hand feed (I have to assume) for this finish cut, I believe would
be ugly.

EVguru
02-01-2010, 03:20 PM
My metalwork teacher would have poured scorn on anyone who couldn't achive a consistent finish with hand feed. We were expected to face 4" diameter and turn 6" shafts. I can still do it 25 years later and indeed have to on the knackered ML7 at work. I don't LIKE having to do it and would always opt for a lathe with self-acts, but it's really not that hard, just dull and tedious.

Hot Bob
02-01-2010, 03:37 PM
I'm thinking that turning down the 4MT arbor on the shell reamer is probably the best way to go. This bore is for a 2" tapered roller bearing race. Accuracy needs to be +0, -.001. I know that a 2" shell reamer doesn't exactly get me that accuracy but I've found that if I burnish the edges of the cutter down with a piece of drill rod, I can get there. I've never cut a MT before. Would it be best to take it to a grinder or is it something I should be able to do myself?

Bob

smalltime
02-01-2010, 04:55 PM
You could try to get a BIG tap wrench on the shell holder and float the reamer on a center in the tailstock.
You just need to stop the spindle as the reamer breaks thru.

It's quick, and you probably already have all the stuff.

whitis
02-01-2010, 07:38 PM
I'm wondering if anyone has any ideas that I haven't thought of on this. I use a Nardini MS1440 lathe. I need a way to quickly bore a finished I.D. of 2" in 2.25" x .250" wall DOM. The depth will be approximately .750".


Ok, let me see if I have this correct. You have tubing that has an ID of 2.000 +0.000/-0.007 and you want to machine it to something like 2.0000+/-0.0001". While the tolerances theoretically guarantee your ID isn't oversized, they don't guarantee that you can get a continuous 360 degree cut, either, even with no runout. With even a small amount of runout, you may end up with an oblong hole as the ID has effectively been cut twice with two different axes of rotation. You need 2.25"x0.375" wall (or an even bigger unobtainium size if you also need the outside dimension to be precise). If you have a piece in hand you can measure if it is adequate for a one off job but if you need to order, there is no guarantee it will be usable. Other tolerances such as straightness, cylindicity, concentricity, and surface finish might mean that even the +0 ID tolerance isn't assured.

Note that tubing isn't necessarily cheaper than solid rod of the same OD.

http://www.nationaltubesupply.com/technical/DOM_mechanical_tube_tolerances.pdf

EdC
02-01-2010, 07:51 PM
Ok, let me see if I have this correct. You have tubing that has an ID of 2.000 +0.000/-0.007 and you want to machine it to something like 2.0000+/-0.0001".
His tubing is 2.25" OD x .25" wall = 1.75" ID

Hot Bob
02-01-2010, 09:19 PM
Ok, let me see if I have this correct.

No, you do not.