Tool Post Holder

My intuition is that by splitting the holder like I have and as I have seen on all the plans that I have looked at online provides a larger clamping area around the entire post when you tighten the clamping bolt. That's just a guess on my part.
 
Hi Guys,

The pinch clamp is, after drilling tapping size, cut in half so that there is a gap between the two half's.
But before that the clamp is trapped in its hole, and the hole for the post bored, so that the clamp gets the radius machined into it.
If its done properly, only a fraction of a turn on the clamp bolt will lock the whole thing onto the post.

The hole for the holder should be a smooth sliding fit on the post. It shouldn't be tight.

Mick:
Splitting the holder distorts the hole and whilst it works, the post is gripped on two edges.
If you blue the post and lightly nip the bolt move the holder slightly you will see this.

I would bore hole for the pinch bolt first and with the bolt in it's hole then bore the large hole for the post.
Click to expand...
Yes that would be how to go about it.

Tom:
Yes you almost have it ! The two half's of the pinch bolt clamp together, there is no expansion.
 
Almost had a major screw up today. I was down to the last couple of cuts as I was sneaking up on the correct size of the center hole. I was moving the crossslide in .001 increments to take off .002 at a time when I inadvertently moved the crossslide .011 equating to taking off .022. When I saw how deep the cut was I knew something was wrong and stopped the cut. Luckily I was only in about 1/4." Found my error and finished the hole getting a good fit for the remaining portion of the hole. The oversize portion of the hole is about .014 oversize.

What should I do about the portion that is oversize? One thought is to put some JB Weld in the oversize portion and then machine it to fit. I don't know if the JB Weld would stick long term. I could also use my welder to lay some beads in this area and then machine the beads to the correct fit. Or I could do nothing.
 
Hi Mick,

1/4" (6 mm) I would do nothing ! It isn't going to make any real difference, 14 thou naw...

I try to avoid sneaking up on a size if I can. Too easy to overshoot as you have found out.

Anyway does this drawing help ?
Norman-002.jpeg
Note that this split clamp pin diameter is not set in stone. The end on drawing shows a diameter of 14 mm, only because I happen to have some drill rod that size. Also the bore is drilled tapping size for M6, but I've shown it as a 6 mm hole.
 
Thanks Baron, The drawings definitely help. I am going to make at least one of the holders per your drawing.

I have to sneak up on a hole to get the correct size. I tend to measure holes slightly under their actual size. If I went by my measurements the holes that I bore would all be oversize. At least for now. Maybe someday I will be able to measure a hole to it's actual size. Or get to a point where my measurements are consistently under size by the same amount.
 
Hi Mick,

Are you boring with the lathe or the mill ?
How are you measuring the bore ?
 
I am doing the boring on my lathe. Don't have a boring head for my mill/drill. I use a telescoping gage and a micrometer to measure the ID of the hole that I am boring. I am getting better at it. I now get consistent measurements. My measurements are smaller than the actual ID. How do I know this? As stated in a previous post my measurement of the ID of the hole is smaller than my measurement of the OD of the post yet the holder fits on the post. So the ID has to be bigger than my measurement.
 
Winegrower said:
I hope everybody considering a four way will check out the inexpensive wedge type QCTP and holders available from many sources, say for example,, CDCO tools. The capability and ease of use, coupled with the low cost of more holders and styles (boring, knurling, etc.) are hard to beat.
Click to expand...

100% on board with this. I have the CDCO wedge tool post with 7 holders for ~$100. Nice quality and I can take my tools on and off and they repeat to the same position within a tenth or two. It makes life so much easier. Plus the height adjustment screw means you don't need to ship. Some argue that there is a loss in rigidity to a small extent, but I haven't found this to be an issue even when doing heavy machining of alloy steels.
 
I made the Norman style QCTP, too. The version with the single slit, not the split clamp. Mine took a lot of "oomph" to tighten on the post as well. To address that I drilled a 1/8" diameter hole on the other side of the holder, located halfway between the bore and side of the holder. Then I cut another slit down to the hole. The rounded section is used as a stress relief. This mod made it much easier too secure the holder to the post.

Here's a photo showing my build. It's installed on a 7x12 mini lathe. I normally do a lot more facing cuts than threading so the compound is set parallel to the ways. The post is CRS, the holder is 6061 aluminum.

my_QCTP.JPG
 
Hi Homebrewed,

Looks nice !
You have discovered one of the issues with using a screw to clamp in that way.
I think that all the articles showing toolpost designs, using a screw to clamp, in that fashion, have done it that way because drilling a hole and cutting a slit is easier than making a proper spit clamp.
 
You must log in or register to reply here.
Back
Top