Right type of screw to hold inserts on a Komet boring bar

ballen · Sep 7, 2017

Hi,

I just bought a couple of used boring bars (left one shown, right not shown). These are 18mm diameter. I've ground a small clamping flat on them and will use them directly in a Wohlhaupter UPA3 boring head.

Although the bars are mirror images of each other, they came with different M3.5 screws. The one on the left has a taper head, IP15. The one on the right is flat head and T10. Which type of screw is correct? Does it depend on the inserts? It appears that the angle screws are available with a 55 or 75 degree angle. How to decide which angle is right?

The inserts are from Walter Unisix, type W28 34000.0464 BK64. The holes have a step and a rounded shoulder but are not tapered inside.

I am pretty sure that the flat head screw (which does not positively locate the insert) is incorrect but would appreciate confirmation before I order some screws.

Cheers,
Bruce

MattiJ · Sep 7, 2017

Very strange looking insert holes. Maybe these are some older manufacturer specifics..
What does the insert package say?

Gordon B. Clarke · Sep 7, 2017

Are you certain it is M3.5 and not 6-32 UNC? It is after all an American product.

ballen · Sep 7, 2017

MattiJ said:
Very strange looking insert holes. Maybe these are some older manufacturer specifics.. What does the insert package say?

Just edited my post to add this info. They are W28 34000.0464 BK64 from Walter. Holes have a rounded shoulder inside but no taper.

ballen · Sep 7, 2017

Gordon B. Clarke said:
Are you certain it is M3.5 and not 6-32 UNC? It is after all an American product.

Hi Gordon! I thought that Komet was German. In any case, yes, I tried a 3.5mm screw and it fit well. So unless 6-32 is a dead ringer for M3.5, I'm 99% sure that it's metric. Cheers, Bruce

PS: here is a similar insert (same overall style and hole style): 17762233 KOMET UNISIX Drehwendeschneidplatte WOEX P25M | HAHN+KOLB Werkzeuge GmbH. Here is another: KOMET - Wendeplatten Unisix W28 34.4 P25M

MattiJ · Sep 7, 2017

Gordon B. Clarke said:
Are you certain it is M3.5 and not 6-32 UNC? It is after all an American product.

What makes it american?
Komet is german, op is german and Walter is german

CarbideBob · Sep 7, 2017

Flat head.
It's a trap pocket so no need for screw locate which would just mess things up.
Do not use taper head screws with this insert. They will bind, come loose, break inserts, and generally behave badly.
It's a design compromise for a screw down trigon. (a shape which sucks in so many ways for location)
In this rare case the screw hole is actually central to the pocket so locating off the bore which is never perfectly centered to the IC is a no-no.
Here one wants the walls to do all the work.

Standard ISO partly cylindrical holes work with a wide range of taper angles. This is not that type of insert hole.

Komet gets away with this as their standard manufacturing tolerances are tighter than the industry average.
Your pictured pocket is one of the most hated by people who have to actually cut, measure, record and hold a process control on them.
Bob

MattiJ · Sep 7, 2017

Me thinks that you need Komet-special screws.
Or maybe there is some old DIN standard for these..

ballen · Sep 7, 2017

CarbideBob said:
Flat head.
It's a trap pocket so no need for screw locate which would just mess things up.
Do not use taper head screws with this insert. They will bind, come loose, and generally behave badly.

Thanks for the advice!

Does this also mean that the screw should be snug but not torqued to the max, so that the insert can slide to the back of its pocket?

CarbideBob · Sep 7, 2017

Screw should be tight to the max spec. or a good feel.
The insert will find the walls it wants to use on the way in.
Bob

ballen · Sep 8, 2017

Bob, I looked on the Komet web site and it appears that they recommend screw N00 57521 for these inserts. All the pictures that I can find on the web (KOMET - Ersatz-Klemmschraube N 57521 M 3,5x7,3 f. Klemmdrehmeissel Kat.-Nr. 18835-18838, for example) show this with a tapered head. Perhaps the pictures are generic, and the screw looks different, or perhaps this recommendation is wrong. I've written to Komet to ask. Cheers, Bruce

MattiJ · Sep 8, 2017

ballen said:
Bob, I looked on the Komet web site and it appears that they recommend screw N00 57521 for these inserts. All the pictures that I can find on the web (KOMET - Ersatz-Klemmschraube N 57521 M 3,5x7,3 f. Klemmdrehmeissel Kat.-Nr. 18835-18838, for example) show this with a tapered head. Perhaps the pictures are generic, and the screw looks different, or perhaps this recommendation is wrong. I've written to Komet to ask. Cheers, Bruce

Most of the Komet inserts in recent catalogs appear to have rounded shoulder on the hole. Yours look like to have pretty sharp 90 degree shoulder?

ballen · Sep 10, 2017

Bob, Matt, you are both right. I just got some new left-handed inserts for the left-handed boring bar. Indeed these have a rounded inner shoulder, and the recommended screw is one with a tapered head. But the older Komet Unisix W28 34000.0464 BK64 inserts have a square inner shoulder, which is different. Does anyone know of a source for high-quality M3.5 "flathead" screws, about 8-10mm long, with a T10 or IP10 head? Cheers, Bruce

MattiJ · Sep 10, 2017

does DIN7984 head fit?

(not sure if its any help, didnt find any source for that in size M3,5)

Gordon B. Clarke · Sep 10, 2017

MattiJ said:
What makes it american?
Komet is german, op is german and Walter is german

I thought this but seems very "international"

KOMET of America - Finish Boring

Maybe they have only one version regardless of country of origin/manufacture.

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Right type of screw to hold inserts on a Komet boring bar

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