Lathe Screw Holder

[eweb101]

I thought I’d try to my hand at tool-making. I’ve only ever made one other tool, something I call “Marv’s Rounding Jig”, although I think everyone calls it that.

I’ve been shortening a lot of screws lately with the bench grinder and have problems cleaning up the threads after I grind them down. I found this project from ClickSpring that looked like it would make shortening and cleaning up screw threads a lot easier:http://www.clickspringprojects.com/screwhead-holding-tool.html

Started with a 3/4 inch nut and bolt from mcmaster/carr


Sawed off its head:



Chucked it up and turned down most of the thread. I turned it down to 9/16"because it seemed like a convenienet size and I have a 9/16" ER32 collet.




Put it in that 9/16” inch collet and cleaned up the thread. I still have a partial thread on the end that I can’t figure out how to get rid of though.



Screwed the nut on and cleaned up the end



I then superglued a 1/16” piece of brass onto the nut, put the nut/plate into the vise and drilled three 3-48 tap-sized holes.  The nut is not visible but it is under the plate



Added heat to separate nut and plate and tapped the 3-48 holes. Not shown but also opened up the holes in the plate to 3-48 clearance size:



I tried to screw the plate to the nut with the 3/8” flat head screws that I had on hand, but the screws were too long so I used button-head screws temporarily.  I always get the math wrong on how deep to drill tapping holes. I know I have to account for the tip of the drill bit and the tip of the tap, but I never add enough extra distance so that I can tap deep enough. Even when I use a bottoming tap, I can’t get right. Doesn’t matter though, shortening the flathead screws can be my first project with this new tool


Next step was to trim the plate to the right size on the micromark belt sander. It still looks a bit rough. I need to figure out how to file some chamfers on the brass plate and make it look pretty.


The final step in making the body of the tool is to drill a hole in the center to accept collets. Since the largest size screw I want to use this tool for is 1/4-20 I chose 3/8” inch for the hole:



I forgot to take a picture while the assembly was on the lathe, but here are the parts at this point:

[eweb101]

Now for every screw size I want to work with, I have to make a collet. The first collet will be for 3-48 screws.

I chucked up some 5/8” brass rod and turned down 1/16” to 3/8” diameter.



Next I drilled for clearance for a 3-48 screw. This is the first time I screwed up on the collet. I used a #37 drill which is what the charts say is clearance size for 3-48. It ended up being way too loose. I’ll use a smaller drill next time.

Then I parted it off and made my second mistake. I thought I could part it off and clean up the face cut by the parting tool either on the lathe or on the mill, but there wasn’t enough to hold onto. I’ll have to think through the sequence of operations for the next collet so I can get both ends faced.

Here is the finished collet. As noted above,it is a little too long.



Now that I’ve finished the body of the tool and one collet, here is how it looks with a 3-48 screw in it ready to be put  in the lathe



And with it chucked up in the lathe:



I need to shorten the screw by 1/8” and the clean up the threads on the end. I tried using a cutting tool to cut off1/8", but that just bent the screw. Next I tried using a parting tool and had better luck but still bent the screw a little. I’ll have to play around with tools to find the right one. Next I took the whole assembly to the belt sander and held the screw against the belt. This worked perfectly. I then rechucked in the lathe and used a small boring bar to clean up the thread and add a chamfer.

I’m really happy with how this tool turned out. I need to figure out a better sequence of operations to make collets and I need to figure out the right lathe tools (carbide/inserts/hand ground/whatever) to work with small screws, but other than that, this project has been a success.

[Flyboy Jim]

Nice tool. I made one myself a few months ago and still need to make some more collets for it. I have some runout with mine that I'm not quite sure how to deal with.............or if that's even a big issue considering its intended purpose.

Jim

[10KPete]

Brilliant!!! Absolutely brilliant!! A simple solution to a common problem usually solved by complex tooling....

Gonna make one.   

Pete

[Zephyrin]

Very nice tool, I have one I made from a plan by John Wilding in a small book I have  "Using the small lathe", brilliant book, with lot of useful tools mainly for clockmaking, pretty similar to the clockspring site, but on paper, and in black and white !
very useful too for screws up to M4. But not convenient for large batch, since you have to stop and restart the lathe !

[eweb101]

Very nice tool, I have one I made from a plan by John Wilding in a small book I have  "Using the small lathe", brilliant book, with lot of useful tools mainly for clockmaking, pretty similar to the clockspring site, but on paper, and in black and white !
very useful too for screws up to M4. But not convenient for large batch, since you have to stop and restart the lathe !

I tried ordering that book last month from ritetime publishing. They stopped responding to email after I sent them my credit card info. Maybe they're on holiday. From what I can tell, there is no other way to obtain the Wilding books.

[mklotz]

The tool you made is normally termed a "lantern chuck".  If you plug that term into Google Images, you'll see pictures of many variants on the theme, including one that looks remarkably similar to the one you made.

A parting tool is, IMO, the wrong tool for shortening slender screws.  A jeweler's saw or a thin cutoff disk in a Dremel or Foredom works very well for me.

[Hans]

I also liked Crispin Cousin's simple screw holding bushings for what appears to me to be the same purpose.... but perhaps I am missing something.

[youtube1]https://youtu.be/AmS73LsDOmI[/youtube1]

Also, I highly recommend his channel. Not only do I learn a lot from this young man, but it is refreshing to find someone his age who shows not only interest and skill in machining and model engineering but a maturity far beyond his years.

~Hans

[Jim Nic]

Nice tool EWEB.  A small modification suggestion - make  the part of your collets that protrude from the nut portion such length that the finished length of the subject screw is just a thread or 2 longer than the collet.  Then the screw will be supported and have less tendency to distort when being machined and you will be able to clean the thread end with a small file while it is still turning, observing suitable precautions to avoid clothing, hair, jewellery or anything else getting caught in the moving bits. 

Jim

[Lew Hartswick]

I made these for a lot of sizes from 1/2-13 down to 10-32 . They work for long normal screws as well as "all-thread" but wouldn't do for short ones.
   ...lew...

On the other hand if you put a nut on first and put the screw in with the head out, cut it off with a thin cutoff tool when the nut is removed it'll clean up the thread.

[eweb101]

Nice tool EWEB.  A small modification suggestion - make  the part of your collets that protrude from the nut portion such length that the finished length of the subject screw is just a thread or 2 longer than the collet.  Then the screw will be supported and have less tendency to distort when being machined and you will be able to clean the thread end with a small file while it is still turning, observing suitable precautions to avoid clothing, hair, jewellery or anything else getting caught in the moving bits. 

Jim

That's a good idea. Of course it means I have to not only make collets for every screw size, but also for every screw length.

[eweb101]

The tool you made is normally termed a "lantern chuck".  If you plug that term into Google Images, you'll see pictures of many variants on the theme, including one that looks remarkably similar to the one you made.

A parting tool is, IMO, the wrong tool for shortening slender screws.  A jeweler's saw or a thin cutoff disk in a Dremel or Foredom works very well for me.

I was hoping that by using a parting tool, it would be an easy way to cut the screws to an exact length, but you're right, it doesn't work so I'll need to use a jeweler's saw or buy myself a dremel tool.

And thanks for the plans on how to make the rounding jig. It has saved me so much time by not having to drag out the rotary table every time I want to make a curved surface.

[sshire]

I watched Crispin's video last night. The tool was very clever. Parts off the screw and chamfers the end of the threads. Worth a look.

[mklotz]

The tool you made is normally termed a "lantern chuck".  If you plug that term into Google Images, you'll see pictures of many variants on the theme, including one that looks remarkably similar to the one you made.

A parting tool is, IMO, the wrong tool for shortening slender screws.  A jeweler's saw or a thin cutoff disk in a Dremel or Foredom works very well for me.

I was hoping that by using a parting tool, it would be an easy way to cut the screws to an exact length, but you're right, it doesn't work so I'll need to use a jeweler's saw or buy myself a dremel tool.

And thanks for the plans on how to make the rounding jig. It has saved me so much time by not having to drag out the rotary table every time I want to make a curved surface.

I have a tiny, self-ground cutoff tool about 1/16" wide that I might try on a #4 screw if it was held really rigidly but for anything smaller I put the screw in my copy of Elmer's hand vise held in the bench vise and apply the jeweler's saw or cutoff wheel.  A quick touch to a sanding disk bevels the cutoff end and I'm done.

I've fitted Elmer's vise with a length stop that allows me to cut multiple screws to the same length.



Yes, the rounding jig is one of my "best sellers".  I'm pleased that you like it.