Saturday, January 21, 2012

Video: Tapping Massive Tail Vise Nuts

The first version of the Benchcrafted Tail Vise used a hex nut bolted to steel angle. While this was functionally good, the design was later refined to allow more vise capacity and easier installation.


Thus was born the massive 1" thick nut that we currently use. This nut starts out as a solid chunk of free-machining steel. Each block is sawn to rough length, then the milling begins. Each end of the nut is milled to precise length. Although this serves no functional purpose in the finished vise, it allows accurate positioning for the other operations that the nut must go through. Plus, it makes for a nicely finished part when you take it out of the box. The pilot hole for the acme tap is drilled and then a large chamfer is cut around each side of the pilot hole. Finally, the two holes in the bottom edge are drilled and tapped for the cap screws that hold the sliding plate to the nut.


Then the blanks are tapped with a 1 1/4" x 4tpi left-hand acme tap. And that's where the interesting part happens. Acme tapping removes huge amounts of material, so acme taps are usually two-stage. The first section of the tap is for roughing in the profile, and the teeth reach to near full depth, but they are narrower than the finished thread. A short "no cut" section is followed by the finishing portion of the tap which takes the threads to final dimension. If you've ever tapped steel before you know that it takes some force to turn the tap (even with a small 1/4-20 tap) and there is always the risk of breakage. Taps are easy to break. So when tapping by hand you reverse the tap every turn or so to break the chips.This is impossible when tapping acme thread. The thread needs to be cut in one shot. So to help clear chips the tap is flooded with cutting fluid. If a chip gets jammed, the tap can break. And a couple weeks ago, that happened. We had a tap break even at the slow speeds that we tap at, and the tool launched itself across the shop. Acme taps are huge, and when they break they make a nice sharp end that wants to lodge in soft flesh. Thank God, no one was injured. This part is probably the most "touchy" part of our vises to make. It's always a tense day when Tail Vise nuts gets tapped.

Here's a video of the process.

11 comments:

  1. I never knew so much hand work is involved. Thanks for posting. Makes me appreciate even more!

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  2. Why don;t you have some sort of guard around the tap? The best way to be safe is to never say we were lucky.

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  3. Great to see some of the work that goes into making these products.

    I too however am worried why there isn't some sort of guard on that machine? When operating it, Jim seems to stand in a very precarious position near the tap. Or perhaps I'm missing something here?

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  4. Same reason most of us don't have guards on our table saws I suppose. The tap didn't actually get launched. I used a little creative license there. Just checking if you were paying attention. ;-)

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  5. When I see these images, I REMEMBER MY FRIENDS AND RENATO ROBERTO THE WORK, AND TO TURN TO THE MILLS. IN PARTICULAR, AND RENATO BRAVISSIMO Many experts. VIDEO! THAT SAY SIMPLY WONDERFUL! THANK BENCHCRAFTED, I always appreciate YOUR PLEASURE WITH WONDERFUL VIDEO AND IF POSSIBLE, SEND THOSE OF METAL PLANERS. WONDERFUL!

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    Replies
    1. Excuse me, MY LAST COMMENT, ANONYMOUS AND 'SIGNED BY MR. PHILIP LAI

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  6. Ron & Jameel,

    I cannot remember when I have enjoyed watching any videos as much as I have these. Really well done and fun as well. This answer brought to you by someone wishing for pork. :o Fred

    As published on Ron's blog also.

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  7. VERY interesting. Obviously your equipment is high end and expensive. Video's and posts like this go a long way, in my mind, to making a case for your costs and quality.

    The next bench I build I'm getting all my gear from benchcrafted along with your split top roubo plans.

    Nicely done.

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  8. thanks for the post, and really glad that you did post that, because machining is not cheap, and all i can say i cant wait till i design my bench or should i say i cant wait till i buy your plans ,, anyway very nice and love your bench a lot:)

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  9. Darn, now that's a lathe! Nice work with all of the videos, keep em coming!

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  10. Michael,

    Actually this is a fairly old lathe that's used for the tapping. Sometimes the "old iron" is hard to beat. Many of these great old machines are getting scrapped, when they excel for certain tasks. While the machine might not be worth much on its own, the machine coupled with the craftsmen's skill is where the real value lies.

    Glad you all enjoy these. We'll try to do more this year.

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