Switching from 3 jaw to 4 jaw chuck

[mriplaybass]

OK, so I am just about to head out into uncharted territory, and start my first simple project. I thought that I had pretty well figured out what I needed to do, but all came to a screeching halt. I want to turn part of a 1" piece of bar stock down so that it will look like an old fashion square head bolt. I'm so proud of myself knowing that I needed to change over to a 4 jaw chuck to turn square stock. I removed the 3 jaw and prepared to install the 4 jaw when I discovered that the 3 jaw had a bigger threaded diameter than the 4 jaw. I looked among the many different parts that the previous owner included, and found the correct sized back plate. Problem is, the chuck has 4 mounting holes and the back plate only has 3! Upon further exploration, I see that there is an adapter on the head stock which I would assume if removed, would expose the correct diameter for the 4 jaw chuck. But I can't get it off!! There are 3 holes drilled around the shoulder of the adapter that look like some sort of spanner wrench with round pegs might fit into. Am I on the right track? and how do I know what type of wrench to get?

 

[markba633csi]

OK, try this: First, apply a liberal amount of penetrating solvent like liquid wrench or homemade juice such as 50/50 acetone/ATF
Wrap a couple layers of cardboard on the assembly and secure with a large hose clamp. Using channel-locks or vise grips, try to remove the adapter. You might have success whapping on the grips with a 2X4 if firm tugs don't do it. I hesitate to recommend engaging the backgears since gear teeth can be broken. Wedging a piece of wood or a rag into the pulleys is a less risky way to immobilize the spindle. A bit of heat might help, but be careful of fire. Use a light bulb or stick a soldering iron in the spindle. Be patient, it may take extended soaking over a couple days
-Mark

 

[mikey]

Measure the ID of the holes. The spanner you use must have a pin that will fit in the holes so they are called Pin Spanner Wrenches. Personally, I prefer hinged pin spanners as opposed to the rigid ones. Looks like this one.

 

[mickri]

I have a similar adapter that I made for one of my chucks. It can be a pain to get off. I now put anti seize on the threads whenever I use it. If you can't wait to get a correct size spanner wrench you could sacrifice one of the holes. First like suggested above apply liberal doses of your favorite penetrating solvent and let it soak over night. Put something that fits in the hole



and give it a good whack with a hammer right next to the adapter.




One good wack is better that a bunch of lighter taps. You will have to hold the pin when you wack it. Not enough hands to show that in the picture. And don't have the back gears engaged. You could break some of the teeth.

 

[mriplaybass]

Thanks for the ideas. I tried a strap wrench, that didn't work. Tried the punch in the hole whacking it with a hammer........broke the punch! I didn't try the hose clamp since the strap wrench didn't work, but I did soak it over night with PB Blaster.
I ended up making this:


Two hits with a hammer and it came right off!
But now I have hit a wall with my project. I don't think that the previous owner ever used the 4 jaw chuck. The threads on the back plate don't match the spindle. Guess I'll be watching eBay!

 

[JimDawson]

The threads on the back plate don't match the spindle.

Time to make another adapter.

 

[mriplaybass]

That's a bit advanced for me. I am still learning what all the levers and cranks do. Plus, this lathe is the only precision machine that I currently have, so I am pretty much forced into looking for a pre made one that fits. Is there a number based on diameter and thread pitch? or do I just look for one based on spindle diameter and thread pitch along with spacing of the 4 bolts that hold it to the chuck?

 

[mickri]

Making an adapter is not that difficult. I am a newbie at this hobby too and have made two adapters so far. One that I call a chuck for my ER32 collets and the other shown in the pictures posted above was for a 4 chuck.

What type of lathe do you have? That will help people to give you suggestions.

Both of my adapters were made using a 3 jaw chuck. The operations involve basic turning and boring to diameters and external and internal threading. When I was learning how to operate my lathe I used PVC pipe to practice on. Then progressed to ordinary steel pipe. The diameters that you turn to and the thread pitch are not important. You are just learning the motions and getting used to your lathe.

When you get to making the adapter you will need to measure the threads and the OD on the lathe spindle and the threads and ID on the chuck. This will determine what diameters you have to turn and bore to and the thread TPI that you have to cut. Here is a link the my thread on making the adapter for the 4 jaw chuck. https://www.hobby-machinist.com/threads/chuck-adapter-backing-plate.81042/ It should help you out on making an adapter.

Have fun with your project.

 

[mriplaybass]

Good thread mickri. My 4 jaw chuck is not threaded, and relies on an adapter which threads to the spindle and is held to the chuck with four 7/16" bolts. I worry about being able to drill these holes symmetrically given that I do not have a mill or any other precision drilling machines. I tried to do some threading, and was very pleased that I set out to cut 20tpi, and actually achieved that. But all that showed me was that I was able to figure out the lathes settings. I did not even use a bit ground for threading. I only cut in far enough to see if it would match my thread gauge. I do not yet know how to cut the large threads that the spindle has, or what kind of bit to use to make the very coarse threads. I have not yet attempted to grind any of my own bits. If I am measuring correctly, it looks like 7tpi is what I am going to have to cut. The lathe is a Hamilton. 15x32

 

[Twirpunky]

. I want to turn part of a 1" piece of bar stock down so that it will look like an old fashion square head bolt. I'm so proud of myself knowing that I needed to change over to a 4 jaw chuck to turn square stock.

You do need a 4 jaw for lots of work. Good practice to use it.

Here is a better and faster way to make square head bolts that look like old ones.

1. Heat up the head of a standard bolt (until red) that has the size and thread you already need. (Even lag bolts) Hang on to it with tongs or vice grip by the thread.
2. If you have an anvil, use it. If not, clamp a piece of heavy steel in your vice and position the head bolt horizontally on the flat surface with one of the points up and the other point on the flat surface.
3. Whak with hammer to flatten the top and bottom points.
4. Rotate 90 degrees and whak some more until you have a square.
5. Repeat step 4 until you have the size of square you want.
6. Drill a hole in a heavy piece of flat stock steel the size of the bolt you are making. (threaded portion)
7. Put your squared bolt in the hole all the way to the head and reheat the head.
8. Hit the head of the bolt with angle blows 4 times. One time on each square side of the head at an angle. This will give you a Pyramid looking top with a square head bolt.
9. Wire brush while still hot.

I do some ornamental Iron working as a hobby and have made at least a hundred of square bolts like this.

D