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A Tailstock Crotch Center for the Lathe

by Russ Harman

I started this metalworking project last winter because I have always thought it would be handy to have a simple way to cross drill round stock in my shop.  I had planned initially to send this to Tyler for publication but Mr. James Instone beat me to the punch with his fixture for drilling holes in round stock.  After seeing his version I finished mine and successfully used it to put tee handles in my new chuck keys.

Mr. Instone’s fixture seemed to be popular and well received and since he invited others to send in their version of the same idea, I decided to share mine.

Tailstock Crotch Center with Drill Guides - Free Metalworking Project

Tailstock Crotch Center - Side - Free Metalworking Project -

I have always considered drilling holes in round stock to be a time consuming bore.  It seems to take a lot of time and effort to find the centerline just to drill a hole. The process is great when it works but irritating as hell when slightly off center, which is often the case when I try to hurry and “eyeball” it. Then every time I look at something I’ve cross drilled off center I am reminded of my laziness. Hence the necessity for my tailstock crotch center.

The whole project is constructed out of steel from the scrap bin, as is typical for these types of projects.  The cap screws came from the hardware store and the #2 Morse taper arbor was ordered from Shars for $6 plus freight. Which I consider cheap for what you get, especially considering how much work it would take to grind an accurate arbor myself.  In fact, I ordered two additional arbors just to have on hand for future projects. Amazon also sells them for $8 with free shipping.

Tailstock Crotch Center - Complete - Free Metalworking Project -

By using the #2 Morse with ½”-20 threads as a base unit I can easily adapt this fixture to my lathe head or tailstock, mill with R8 adaptor, or drill press.

By taking out the taper and putting in one of the large cap screws I can clamp it in a vice, lathe chuck or collet fixture.

Tailstock Crotch Center - Back - Free Metalworking Project

By replacing the arbor with a cap screw the fixture can be used in a vise, lathe chuck, or collet.

I used long small diameter cap screws for securing the clamping plate to accommodate larger diameter material.

I also made a storage box for my new tool.

Tailstock Crotch Center Storage Case - Free Metalworking Project

The right hand side of the box contains four drill bushings measuring 1/8”, 3/16”, ¼”, and 5/16”.  For other odd sizes I can simply use the clamping plate without a bushing and use a center drill to accurately locate my hole.  I tried to think and cover all the bases to make the fixture as universal as possible so it was not just another box taking up space in the drawer.

 Making the Tailstock Crotch Center

The first item of business was to cut a 1” disk off a 3 ½” diameter piece of round stock.  I then placed the disk in my three jaw chuck and faced it off.  Next the part was center drilled, drilled through, and chamfered in preparation for the tapping operation.  After tapping to ½”-20 the Morse taper adaptor was screwed in and all other lathe operations were done with it in place.  I took the chuck off and put a #3 to #2 adaptor in place so it would fit the taper in the headstock of my lathe.  I then faced the second side and rough turned the diameter.

To make the clamping plate a flat piece of 3/16” stock was screwed to the face of the part, center drilled and a .050” relief machined for the drill bushings.  The edges were then turned down to match the diameter of the body of the crotch center.  Next I removed the piece from the lathe and after removing the taper and clamping plate I secured the body of the crotch center in a tilting drill vice at 45 degrees to cut the v-groves.  Both the deep and shallow grooves were cut using a 5/8” end mill.  I like using larger mills whenever I can due to the extra rigidity they offer.  The drill bushings were then turned from oil hardening drill rod I which always keep on hand.

Making the Storage Box

The box bottom is a 2”x6” that was squared up on a jointer.  The cutouts were made and the holes drilled to accommodate the included pieces.  Cutouts for the Morse taper were made with 1/2” and ¼” ball end mills.  The box sides were made from 3/16” mahogany wrapped around the base.  The lid was then glued on and after it set up, I flushed up the edges with an orbital sander.  The lid was then cut off the box with a table saw.

Tailstock Crotch Center Storage Box - Free Metalworking Project

I like making boxes this way as there are no dimensions to match since the lid is identical in width and depth to the base.  Just remember to work as if you are inside the box so you leave clearance for the contents.  Mount hinges, apply stain and varnish, and presto! You’ve got custom fitted storage box.

Boxed items are safer, more organized, and just plain look COOL!  After all, everybody likes to look inside a box for the treasure to be found!

Now get out there and keep the SWARF flying!

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About Uncle Russ

Retired electrical contractor. Really always wanted to be a machinist so I am self teaching and having a great time.

7 comments

  1. Congratulations, Russ — I have been thinking of buying/making one of these for some time. I like your use of a ready-made arbor. Thanks for your mention of my project.

     

    joutrock (James Instone)

     

  2. Excellent project Russ!

    Quick question, it looks like one of the large cap screws is ground and one isn’t. Is that the case? If so, for what purpose? For precision when you mount it in a collet? And … when would it be useful to mount it in a collet? That one has me puzzled. I can’t think of an application where I would need to do that. 

     

  3. Mr. Tyler:

    The cap screw that appears to be ground is actually just turned so it would better fit of all things, a collet bushing.  I used my indexable collet holder to hold the work for cutting the “V” grooves in the surface.  Tilted the collet holder at  a 45′ angle made cut one.  Rotated the indexer 90′ and made cut #2.  The cap screws are the same thread as the MT adaptor.  Use the head of the capscrew to also hold the fixture in a drill or bench vice.  Just anything I could think of to make it more useful.

  4. Russ,

     

    A clever and beautifully made jig. I particularly like the storage box. Nice touch.

     

    It took me a while to work out how it worked – at least I think I’ve worked it out. Rod to be drilled is sandwiched in the v groove and the cover plate screwed on and the insert screwed in place.  What I can’t work out is how the device connects to the Morse Taper. A couple of photos with the jig in action might help explain things better.

     
    Cheers
     
    Mick Doherty
  5. Mr. Mick:

    The end of the MT adaptor has 1/2″ x 20 threads on the end.  The adaptor merely screws into the back of the large body piece. Same as the two large cap screws used to hold the fixture in a vice or collet so as not to mar the finish on the body.

    In use, remove the two screws lift off plate.  The back of the plate has a recess for the drill bushing to fit flush into to keep the back flat.  The bushing is shown in the second picture installed in the jig.  Place the material to be drilled in one of the “V” grooves and replace the cap.  If screws are too short longer ones are in the box.  The drill guide was included to preclude the need of center drilling to start the body drill.

    You may also center other shapes of stock by resting the material against the two cap screws under the top plate of course.  It will basically center drill anything you can figure out how to put in it!

    Hope that clears it up a little.

    Uncle Russ 

  6. Uncle Russ,

    Thank you for you clear instructions. Penny finally dropped.

     

    cheers

     

    Mick

  7. Love it.  It’s on my list of tools to make. 

    Regards, Al