Norman-style QCTP pinch clamp

[homebrewed]

Message 48 in https://www.hobby-machinist.com/threads/tool-post-holder.69487/page-5 describes the use of a pinch clamp to fix a tool holder to the tool post. I like the idea and want to use it for my next tool holder, but I have a question about making it. Specifically, when boring the hole for the tool post, how is the pinch clamp-to-be fixed in place during that op? It seems to me that there is a pretty good chance that just inserting the bolt in its hole will permit it to turn due to the machining forces. It can't be a press fit because of what it's supposed to do, so how is that accomplished?

I can see something funky like a set screw to hold it in place but dislike the idea of doing that just for machining the thing.

 

[T Bredehoft]

The vertical member is secured by a cap screw into a T Nut. The tool holder is a slip fit on the vertical member, tightened by one or two cap screws tightening across a slit through the tool holder compressing it on the center vertical member.

 

[mickri]

I had the same question about making one for a tool holder for my Norman QCTP. As best as I can tell one end slides on the bolt and the other end is threaded. As you tighten the bolt the two halves come together wedging against the post. For the best result the two halves need to be machined from one piece when you bore the hole in the tool holder. Then cut them apart. That makes each slightly shorter so they can wedge against the post. It is a similar to the quill clamp on a round column mill/drill. I took the quill clamp apart on my mill/drill to see how it works.

 

[homebrewed]

I had the same question about making one for a tool holder for my Norman QCTP. As best as I can tell one end slides on the bolt and the other end is threaded. As you tighten the bolt the two halves come together wedging against the post. For the best result the two halves need to be machined from one piece when you bore the hole in the tool holder. Then cut them apart. That makes each slightly shorter so they can wedge against the post. It is a similar to the quill clamp on a round column mill/drill. I took the quill clamp apart on my mill/drill to see how it works.

I understand how the pinch clamp works, once it's been made. The toolpost itself keeps the parts of the pinch bolt from rotating so it can be tightened up around the post.

My question is regarding its fabrication. The stated method is to have it in place when the mounting hole is being bored, but what keeps the bolt from rotating during the boring step? It could be done by capturing it from both sides with screws and washers (assuming it doesn't protude past the outside of the QCTP) but it will require that end of the QCTP-to-be to stick out past the end of the vise, making for a noncentered workpiece in the vise.

 

[mickri]

I bore the center hole in my tool holders held in a 4 jaw chuck on the lathe. So stick out of the pinch bolt would not be a problem for me. You could tack weld it to the outside of the holder to keep it in place. That is what I would probably do.

 

[homebrewed]

I've decided to use 6061 for my tool holder so a tack weld is not an option, at least not for me. It looks like the best way is to use a temporary set screw to fix the pinch clamp in place while I'm boring the hole, much as I dislike the idea.

My 4-jaw chuck isn't big enough to hold it. If it could, that could be the best approach. But now I'm wondering about using a faceplate. I don't have one but if it looks like that would work, it might be enough motivation to acquire one.....

 

[mickri]

Rather than a set screw I would use a bunch of small washers with a bolt all the way through and use that to clamp the pinch in place. You could start with the pinch almost as long as the width of the tool holder and then cut it down to the length you want.

How big is your 4 jaw? Can you reverse the jaws to get more room? My tool holders are 2.5" long by 2" or 2.25" wide,

 

[homebrewed]

Rather than a set screw I would use a bunch of small washers with a bolt all the way through and use that to clamp the pinch in place. You could start with the pinch almost as long as the width of the tool holder and then cut it down to the length you want.

How big is your 4 jaw? Can you reverse the jaws to get more room? My tool holders are 2.5" long by 2" or 2.25" wide,

My tool holders usually are about the same size as yours. I'll check to see if I can grip one of my preexisting holders with reversed jaws, thanks for the suggestion!

 

[mickri]

I was thinking about modifying one of my holders to use a pinch to try it out and thought of a way to hold the pinch while I machined it. My holders and probably yours have a bolt that screws into one side the holder to pinch the holder together to lock it to the post. You could enlarge the hole for the bolt to fit the pinch but don't bore all the way through the holder. Leave a portion of the thread in the holder. Put the pinch in the hole and lock it in place with the bolt. Then machine the pinch.

 

[homebrewed]

I was thinking about modifying one of my holders to use a pinch to try it out and thought of a way to hold the pinch while I machined it. My holders and probably yours have a bolt that screws into one side the holder to pinch the holder together to lock it to the post. You could enlarge the hole for the bolt to fit the pinch but don't bore all the way through the holder. Leave a portion of the thread in the holder. Put the pinch in the hole and lock it in place with the bolt. Then machine the pinch.

That sounds like it would work OK for changing a slot-type system over to a pinch bolt (assuming you've got enough room for that larger hole).

I'm working on an all-new holder so most likely will reverse the jaws on my chuck per your earlier suggestion. This holder will be a 2-piece design so I can more easily play around with different cutter configurations and orientations.