Tight tolerance bores

[MIL-TFP-41]

Got a part coming up...small production run with the potential of becoming many.

 

has 4 different bores, ranging from 1.380 in dia to 1.850 in diameter. Kicker is all the bores are +.0003 minus nothing....so .0003 total tolerance on the bores. All have true position of .001, however, all the datums can be machined in the same setup as the bores so that doesn't bother me so much. The part is cast aluminum...one of the bores is in the aluminum and the other 3 are in 4130 sleeves that are pressed into the part.

 

The .0003 tolerance does make me raise any eyebrow tho. I have used romicron heads in the past & they are easily adjustable to holding that tolerance. My question is will they repeat toolchange after toolchange?

 

I have my choice of machines to run them on, our Mori NH5000 or the Matts H-plus 405 are the leading candidates.

 

The shop running these previous were having the bores jig ground to size. They also had a 50% scrap rate from position & size problems.

 

So...possible to do consistently with boring heads? any thoughts?

[THEE THAINZ™]

KAISER boring bar

[Joe788]

No problem. The difference between +.0002/-.0   and +.0003/-.0 is HUGE.  You'll spend a couple thousand bucks on the right cutting tools, but as long as you spend a couple thousand more on the right measuring tools, it shouldn't be too bad at all. As long as your bores aren't thin walled - you can actually get extremely good measuring results using the machine's probe. Obviously you'll still need post process measuring, but you'll find pretty quickly that the machine probe on either of those machines is deadly accurate, as long as it's calibrated properly.

[YoDoug®]

I would look at Walter or Mapal padded reamers. I have seen Walter padded reamers in an Okuma vertical holding those kinds of tolerance to a 1.33 CPK in engine cases.

[specv]

Romicron boring heads are great, we bore a few parts with -.0000/+.0003 we also use EPB boring heads for the larger sizes. Does your machine have a slow tool change option? also making sure your tools/spindle are clean is a big deal with these tolerances.

I would use an air gage so you can check for roundness as well as size. 

 

As far as inserts we have found that Korloy polished inserts cannot be beat for getting a good finish in bores.

[Guest]

No problem. The difference between +.0002/-.0   and +.0003/-.0 is HUGE.  You'll spend a couple thousand bucks on the right cutting tools, but as long as you spend a couple thousand more on the right measuring tools, it shouldn't be too bad at all. As long as your bores aren't thin walled - you can actually get extremely good measuring results using the machine's probe. Obviously you'll still need post process measuring, but you'll find pretty quickly that the machine probe on either of those machines is deadly accurate, as long as it's calibrated properly.

^^^

This

[crazy^millman]

Romicron boring heads are great, we bore a few parts with -.0000/+.0003 we also use EPB boring heads for the larger sizes. Does your machine have a slow tool change option? also making sure your tools/spindle are clean is a big deal with these tolerances.

I would use an air gage so you can check for roundness as well as size. 

 

As far as inserts we have found that Korloy polished inserts cannot be beat for getting a good finish in bores.

 

Put these very tools in a place and they guys were amazed they could adjust to a .002mm with just one click. Repeats and does very nice work. I have used many of the systems out there, but really like the Romicron system. Also put polished inserts in with these tools and they did a great job.

[chris m]

As long as your spindle taper is good and the tools are clean, I think the Romi heads will do fine; bored thousands of pieces with .0004 or .0005 tolerance with those.

 

I think it is extraordinarily unlikely that you can bore the same size with the same head in two different materials, though.

 

C

[Joe788]

I think it is extraordinarily unlikely that you can bore the same size with the same head in two different materials, though.

 

 

^It didn't even occur to me that he might be asking this - but that's a good point. I assumed he meant different bores.

 

We use Kaiser heads, not sure of the model. They're about $1600 by the time you buy the CAT holder and the insert holder.  You CAN adjust .0001 reliably, but you need a steady hand and Go Go Gadget vision (or an Optivisor in my case).  If we were doing higher volume, I'd definitely look at the Kaiser, Romicron, or Walhaupter digital unit.

[Del.]

^It didn't even occur to me that he might be asking this - but that's a good point. I assumed he meant different bores.

 

We use Kaiser heads, not sure of the model. They're about $1600 by the time you buy the CAT holder and the insert holder.  You CAN adjust .0001 reliably, but you need a steady hand and Go Go Gadget vision (or an Optivisor in my case).  If we were doing higher volume, I'd definitely look at the Kaiser, Romicron, or Walhaupter digital unit.

If you needed to take .0001 more out of the bore wouldn't it still have tool pressure built up and take too much out without backing off and resetting?

[Joe788]

If you needed to take .0001 more out of the bore wouldn't it still have tool pressure built up and take too much out without backing off and resetting?

Yeah if you're trying to rework an existing bore by taking .0001 off, that's a whole other nightmare. I just mean making adjustments from part to part. The smaller Kaiser heads have a very small vernier, but it's very accurate as long as you can see it.

[specv]

Del, it depends on your process, we would normally only leave .005 total for a bore that tight so there won't be much deflection if any at all on aluminum.

[MIL-TFP-41]

As long as your spindle taper is good and the tools are clean, I think the Romi heads will do fine; bored thousands of pieces with .0004 or .0005 tolerance with those.

 

I think it is extraordinarily unlikely that you can bore the same size with the same head in two different materials, though.

 

C

 

Fortunately the 1 bore that is in aluminum is on a size by itself. 4 bores, 4 different sizes. Although 1 bore is only .001 larger than another one......another tool to the pile, another $2000 for a boring head.

[Guest]

If you needed to take .0001 more out of the bore wouldn't it still have tool pressure built up and take too much out without backing off and resetting?

You gotta hone that out IMHO.

[betts]

Since you were already questioning the tool changer aspect I shouldn't need to say it, but the care and attention as described above will be critical.  We did some testing in Makino a61's because we were having orientation problems with an El-Tool RA drill.  The tool changer using factory tolerances doesn't repeat all that well in orientation.  The taper and retention force on your machines shouldn't be an issue when well cared for.

 

To correct our problem we inserted the primary notch that mates with the drive dog and made the tolerance .0015" clearance so that when you put a 1" drill in the RA head it will repeat within ~.001.

 

Like Doug  said we have switched quite a few bored holes over to the high dollar reamers in the last couple years with great success.  Lead time is usually the killer and we have had jobs that we did what we had to for the first run because while the reamers worked great i couldn't get them in today's insane lead times.