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Inserts and their setscrews. On my Iscar insert the profile of the hole is curved. The screw profile is 45 degrees. Point of contact?

rons

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Mar 5, 2009
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I got lucky because my Iscar boring bar has a setscrew thread of 4mm - 0.7 thread. And my stock pile has some of those.
I'm making another setscrew for these inserts and noticed that the original setscrew has a wear mark less than half the contact area.
The real point of contact is a thin ring. The wear area on the screw is wider because the screw moves down as it is tightened.
There is enough metal on the original and custom setscrews for a curved profile. Full contact couldn't hurt.

Does anybody look at this as a problem for vibration. Would the mode of vibration change if the contact was increased?
Is there any material that can be stuffed into the insert hole, dry, and take a measurement from?
 
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If you look closely you will see that the hole in the insert and in the bar do not align. This is so that the insert is pulled firmly into the pocket. Screws are a wear item so need to be replaced occasionally. I doubt you are going to improve anything by making changes. To measure squeeze some soft lead in there and measure off that. Cerrosafe is probably the best for measuring but you may not have it.
 
The stiffness of the joint is driven by the preload and the contact between the insert and pocket. Increasing the contact area between the insert and screw will not improve things.

(Also it’s safe to bet that that screw/insert interface has already been carefully engineered. My guess is the curved pocket is to allow the screw to make predictable contact with the insert even as it bends when it pulls the insert into the pocket)
 
It is an industry standard.
This is a ISO partly cylindrical hole.(for screw heads from 40 to 60 degrees).
See here: https://jennmar.docdroid.com/fbgT1OI/xcal-industires-tooling-catalog-pdf#page=413
(page 413 for the holes, page 412 for the screws)
Contact should be a line around the screw.
Screw hole is offset .003/.005(inch) towards each wall to pull the insert to the walls.
This is important as the standard for position of the hole in the insert is +/-.003 or .006 TIR.
Bob
 
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Thanks CarbideBob.
The question is geared to questioning about the hollow space inside the hole. If it was more packed would the mode of vibration change/
I'm looking at a extension of 5" with a 7" bar, 2" fully held in a little L21 tool holder.
 
No, the vibration is not from the insert clamping arrangement it is from the length and thickness ratio of the bar. However running a bar with excessive vibration will aid in speeding up failure of the screw.
 
It is an industry standard.
This is a ISO partly cylindrical hole.(for screw heads from 40 to 60 degrees).
See here: https://jennmar.docdroid.com/fbgT1OI/xcal-industires-tooling-catalog-pdf#page=413
(page 413 for the holes, page 412 for the screws)
Contact should be a line around the screw.
Screw hole is offset .003/.005(inch) towards each wall to pull the insert to the walls.
This is important as the standard for position of the hole in the insert is +/-.003 or .006 TIR.
Bob
Thanks for that Bob. Next time I make a special holder I will now know exactly where to put the hole.
 
I got lucky because my Iscar boring bar has a setscrew thread of 4mm - 0.7 thread. And my stock pile has some of those.
I'm making another setscrew for these inserts and noticed that the original setscrew has a wear mark less than half the contact area.
The real point of contact is a thin ring. The wear area on the screw is wider because the screw moves down as it is tightened.
There is enough metal on the original and custom setscrews for a curved profile. Full contact couldn't hurt.

Does anybody look at this as a problem for vibration. Would the mode of vibration change if the contact was increased?
Is there any material that can be stuffed into the insert hole, dry, and take a measurement from?
I would try the dog shit that you were trying to measure with your Chinese digital caliper. <wink>
 
So full contact...bad.
A well used screw will grind itself into the cone shape here and do more contact area.
Eventually it will not come out as this hole is rough inside. Then you learn how to drill out screws. :wall:
This is why you toss screws that have much of a wear land.
The other thing if making your own pockets is the interface at the bottom of the wall and floor.
No endmill makes sharp corners down here. There are a variety of constructions here for this problem.
Some positive inserts will have a 45 chamfer on the bottom. Some use a shim seat (NL style). Others need some clear down at the bottom.
Often called a "dirt relief". An undercut or a flat on a positive rake pocket.
Positive pocket. What angle end mill to use? There is a tolerance on molding or grinding this angle. You need to be over it.
Pocket wall height. The rule of thumb here is .010 below the cutting edge.
Why? When you index the tool it may have some stuff on the sides. You want to be below this so that it will seat on the walls.

More to the OP and vibration. As a tool designer I see no advantage to filling the hole. This should be a rigid connection out of the gate.
If your insert is vibrating here something is so very wrong. You will see this with fretting on the pocket walls and scaring on the insert sides.
This does happens when people mistaking put the screw hole on center. (seen that)

These holes are not ground or EDM cut. Why people expect them perfect or inside .001 is beyond me.
For sure we can and will do this for the silly. You do not want to see the price tag.
Bob
(10 cents from the peanut gallery here, many years and still learning. It all looks so simple....Why do I have problems on pocket lock up?)
 
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No, the vibration is not from the insert clamping arrangement it is from the length and thickness ratio of the bar. However running a bar with excessive vibration will aid in speeding up failure of the screw.
Just reading about anti-vibration designs and using up to overhang = 10 x Bar-Diameter.
 








 
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