Criterion Boring Head

sen2two · Mar 17, 2018

I have a 3.00" Criterion Boring Head. The square body type for a .750" boring bar.

The adjustable part (lower half) has become very loose. I can wiggle it easily with my hand. No other noticeable damage. I havnt dropped or abused it. I'm unsure on how to fix this. Anyone here with experience in this?

crazygoat · Mar 17, 2018

Sounds like the gib is loose. try snugging it up.

mjk · Mar 17, 2018

Sounds like its scrap
Box it up properly and send it to me .
I'll send you the postage amount once I receive it......

sen2two · Mar 17, 2018

I didn't see where I can snug up the Gibbs, any tips? I looked for an area that might have adjustment and didn't see it.

mjk · Mar 17, 2018

I think there are small set screws for the gibbs

but you may find a manual if you do a search on the Gooogle

post a couple pics

sen2two · Mar 17, 2018

Figured it out...

Ths 3 set screws on the side. The outer most ones should have a locking nut. This keeps the side body (gib plate i guess) tight. The center set screw gets no locking nut and does the job of locking the adjustment.

crazygoat · Mar 17, 2018

I have never seen a Criterion with nuts on set screws. I always ran them snugged up, never locked down. I have seen them where somebody had locked them down and left divots in them. When you would get close to that spot, the divot try would pull the screw into that spot making them hard to adjust correctly.

Gordon Heaton · Mar 17, 2018

Last I heard, Criterion says to leave the outside gib screws alone once set and use the center to lock/unlock. I've found it essential to lock the slide with the center screw to facilitate consistent performance.

moonlight machine · Mar 18, 2018

You tighten the center set screw till the cross feed screw still moves freely with no slop. you lock the outer screws while making a cut.

rons · Mar 18, 2018

crazygoat said:
I have never seen a Criterion with nuts on set screws. I always ran them snugged up, never locked down. I have seen them where somebody had locked them down and left divots in them. When you would get close to that spot, the divot try would pull the screw into that spot making them hard to adjust correctly.

That is what I don't like about stock set screws. They have a small cup on the end. When locking down the cup will grind into the opposing metal surface like a drill. Not a bad idea if you are locking down a flywheel on a shaft forever. Otherwise you get circular dents. On some sliding mechanisms which are nice and shiny I turned down the points of the set screws and inserted a small disk of teflon or aluminium into the set screw hole. I don't think I would do it for my two Criterions.

mach2 · Mar 18, 2018

Gordon Heaton said:
Last I heard, Criterion says to leave the outside gib screws alone once set and use the center to lock/unlock. I've found it essential to lock the slide with the center screw to facilitate consistent performance.

My 20 year old instructions say just this. I don’t remember the set screws making divots on the sliding parts. Maybe the back side of the gib but not the sliding area. Using center set screw of a gibbed slide works on your lathe as well, old trick still works good.

moonlight machine · Mar 18, 2018

mach2 said:
My 20 year old instructions say just this. I don’t remember the set screws making divots on the sliding parts. Maybe the back side of the gib but not the sliding area. Using center set screw of a gibbed slide works on your lathe as well, old trick still works good.

They don't have gibs as we know them. The dovetail on one side has a cut behind it. The set screws hit this to tighten it without damage to the sliding areas.

mach2 · Mar 18, 2018

moonlight machine said:
They don't have gibs as we know them. The dovetail on one side has a cut behind it. The set screws hit this to tighten it without damage to the sliding areas.

Thanks for that clarification. I wasn’t near mine to take a closer look. In any case the gib screws do not contact the sliding parts or the boring head.

Larry Dickman · Mar 18, 2018

there should be balls underneath the set screws. If the balls are gone, that would explain why it wont adjust correctly

UncleFrank · Mar 19, 2018

As I recall the instructions with the Criterion boring heads say to tighten the outside set screws first when setting the bar. Then the center set screw. To fine adjust loosen/tighten the center set screw only for repeatability. Loosening/tightening all three at once can really mess with repeatability when you're trying to adjust a few tenths.

They don't have to be super tight. On the smaller heads we would snug up the set screws then put a finger on the allen wrench and press down until the wrench started to bend. You'll just have to use judgment on larger heads/wrenches. All you're doing is pushing the gib sideways to hold the dovetail on the movable piece.

+1 on using slugs on the generic style bars. A set screw digs into the cutter body and "self centers" when trying to adjust a few thousandths. We used steel slugs from the punch press shop. They held up better than aluminum in our situation.

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Criterion Boring Head

sen2two

Aluminum

crazygoat

Stainless

mjk

Titanium

sen2two

Aluminum

mjk

Titanium

sen2two

Aluminum

crazygoat

Stainless

Attachments

Gordon Heaton

Titanium

moonlight machine

Diamond

rons

Diamond

mach2

Stainless

moonlight machine

Diamond

mach2

Stainless

Larry Dickman

Titanium

UncleFrank

Cast Iron

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