DTI Clamp

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ctwo
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DTI Clamp

Post by ctwo » Mon May 21, 2012 1:04 pm

I made an aluminum clamp for my DTI - basically cut from square aluminum bar with a few holes. I threaded one end and pressed a socket head screw into the knob.

It works like junk. The DTI wiggles unless clamped very tight (there might be a bur where the cut slot comes into the hole) and the pieces don't hold their alignment very well.

I was wondering if a washer between each surface would help? I was also thinking of cutting some of the material so the bearing surfaces are round, like I did on the handle.

Also, would the slot work better if it was centered? I offset that so there would be more thread.
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clamp.png
clamp.png (6.69 KiB) Viewed 2639 times
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BadDog
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Re: DTI Clamp

Post by BadDog » Mon May 21, 2012 1:56 pm

I would put a small polished steel washer between each layer and see how much that helps. Aluminum on aluminum galls, and even when it doesn't, it still doesn't want to slide unless you hard anodize it. And right now, as things try to move out of parallel through clamping, you are getting all sorts of weird loading depending on orientation.

I would also have put the slot in the center, and if the back side (opposite slot) is very heavy, I have also been known to slot the back side to make a smaller hinge. Then again, I've only made such things in steel. Aluminum, depending on alloy and condition, may be prone to fracture if you get if an excuse (stress risers).
Russ
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ctwo
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Re: DTI Clamp

Post by ctwo » Mon May 21, 2012 3:01 pm

Sounds reasonable. I knew it was not going to be very good, but thought it would at least be workable. I'll throw some washers in there and then consider buying something, maybe an indicol...I'm not getting the right range on this thing anyway...
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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ctwo
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Re: DTI Clamp

Post by ctwo » Mon May 21, 2012 3:23 pm

I suspect this design is not much better...
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clamp2.png
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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GadgetBuilder
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Re: DTI Clamp

Post by GadgetBuilder » Mon May 21, 2012 4:47 pm

If you don't mind using steel for the clamp then consider copying the principle used by Starrett. I made the copy seen below with the part holding the tooth index longer than normal. It seems to hold two rods in a relation similar to the clamp you built.

I use a similar clamp on the QCTP holder for my DTI - it can lock solid but can be left with enough friction so it can be moved into place as needed and still holds fine for indicating. There's a spring inside to provide moderate pressure when the solid lockup is released, prevents it from flopping around unexpectedly when the nut is backed off slightly. I just looked at the clamp on my surface gauge and sort of copied that using material from my scrap box. (Starrett has an extra slit in their clamp but I didn't understand its purpose so I left it out.)

John

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BadDog
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Re: DTI Clamp

Post by BadDog » Mon May 21, 2012 11:34 pm

It's maybe a bit bulkier (though less than the current design image), but another option would be a "split cotter" arrangement. Really strong grip with little pressure, but easily moderated for snug-slip. But on a common screw, it will lock the rods solid long before the pivot even gets close to locking. Might be good, might not...

In any case, I think a much thinner cross section made in steel will see far better results. I've made clamps similar to yours, boring bar bushings, stop clamps, mic/indicator/stop clamps for the lathe bed, all sorts of stuff like that; but all of it from steel.
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Lew Hartswick
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Re: DTI Clamp

Post by Lew Hartswick » Tue May 22, 2012 8:40 am

I think the biggest problem is you have two "springs" in series so unless one of them is completely
compressed the other will not be doing the right sort of clamping.
...Lew...

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ctwo
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Re: DTI Clamp

Post by ctwo » Tue May 22, 2012 8:28 pm

I see some really good points in the comments there. I like the second design only slightly better. The other suggested designs look very good and I'll have to think about how to make them.
Since I had a thin teflon disc laying here, I merely hole punched it with a common paper hole puncher and slapped that in between the blocks - and there is significant improvement in lockup, plus the blocks are easily adjustable when tight, and they hold...
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

dmerd
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Re: DTI Clamp

Post by dmerd » Tue May 22, 2012 9:14 pm

Here is a few that I made.
Attachments
Holders 01.jpg
Holders 02.jpg
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ctwo
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Re: DTI Clamp

Post by ctwo » Wed May 23, 2012 6:27 am

Those are really good. I especially like the second pic, and I think I could even thread those screws... I also drew up this idea. Now I have lots to build.

Thanks
Attachments
clamp3.png
clamp3.png (6 KiB) Viewed 2470 times
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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