Easy build spider for small lathe

[black85vette]

This is how to build a lathe chuck spider for the beginner with a small import lathe. A spider is used to position thin work out near the end of the jaws so you can face it. I used my Harbor Freight 7x10 to show how. First to give credit. I saw something like this on a post by Mklotz elsewhere and decided to make one for my small lathe so it is sized for a 3" chuck. Here is what we are making.

 

[black85vette]

Here I have mounted some 3" rough cut aluminum in the chuck. I intentionally do not push the piece all the way back in the chuck because the back side is not square or straight. I rock the piece as I tighten it to try to get it square with the jaws of the chuck. There will be some gap in the back but that it OK. We will square up everything as we go.

Face the first side until it is smooth all the way across. Flip the piece over and this time push the faced surface firmly to the rear of the chuck until it seats all the way around.

Center drill it just enough for the live center to get its tip into the hole. About 1/8th inch.

Pull the piece out of the chuck, close the jaws down to less than the size of the work piece, then hold the piece against the front of the jaws with the live center in the tail stock. It will need to be firm but not too tight. Too tight and you will warp the piece you are working on. Some people put double sided tape on the face of the chuck to get better grip on the piece.

Then making light cuts, reduce the diameter of the piece until it is smooth all the way around. Now you have a smooth front and the outside diameter is square to it.

Put the piece back into the chuck with the faced side in. Seat it firmly again. I snug my jaws down and then tap it in the center with a rubber hammer. You can put strips of aluminum softdrink can between the jaws and work if you don't want it to get scratched. For this project it does not matter. Now you can face the second side and it will be parallel to the first. This is where you make it the thickness you want. It needs to be about .125 inch less than the height of the jaws. Mine ended up at .515 inches thick. I take mine to within about .005 inch and then flip it over and take the last bit off the first side to be sure they match.

You can use this same method to make flywheels. I have made some as large as 6 inches on this lathe.

 

[black85vette]

Because most of the measurements on this are not critical we can cheat a little. I put some layout dye on the edge of the piece and just scribed next to each jaw. This will give a reference mark for the layout. The center finder square is positioned to line up with the mark and then we scribe from the center to that line. When you have all three done center punch where the three lines cross. Using that punch mark set your dividers to .485 inches and draw a circle. Where the 3 radial lines and that circle intersect is where we will center punch and drill a .5 inch hole.

Again using the center finder square, lay it over each of the lines and with the dividers set to .25 inch scribe a line parallel to the first. Then flip the square over and do the same thing on the other side of the line. You end up with two lines .5 inch apart and parallel to the reference line you started with.

 

[black85vette]

Now its time to drill the 3 holes that we marked. I like to center drill, then use a .125 inch drill and then the .5 inch. Just my preference. Once you have them drilled you can cut the lines from the outside of the disc to each edge of the .5 inch hole. You will end up with 3 slots for your chuck jaws.

In the picture is a piece of brass less than .250 inch thick being faced on the lathe. You can make this hold thinner work by making the spider thicker or putting shims behind the work piece.

There you have it. A useful piece that you can make without great precision or fancy tools.

 

[zeeprogrammer]

I like it! Thanks. I've struggled with working on thin pieces. I know there are some threads that talked about some special or home-made 'collets'(?) but I hadn't seen this approach.

 

[Philjoe5]

Thanks for posting this excellent visual. This is one of those tools that should be in every toolbox and you've made it clear how to make one. Karma to you sir :bow:

Cheers,
Phil

 

[ozzie46]

Thanks Vette, you don't know how many times I tried to face thin stuff without much luck. A point for you.

Ron

 

[mklotz]

If you have a small lathe as shown, you may be able to get away with only one spider offset determined by the thickness of the spider body. For larger equipment you may want to make the spider offset adjustable.

In my version...

http://www.homemodelenginemachinist.com/index.php?topic=1235.msg8925#msg8925

I drilled holes in the spider to accept precisely machined standoffs. With several sets of such standoffs, one can have a variety of offsets to match different jobs. Note that each standoff has an integral tenon that fits in the spider hole when the standoff is in place. This is an important safety feature - it ensures that the standoffs are locked in place when the chuck is turning and that they can't fly loose and cause damage.

I considered drilling and tapping the spider for threaded standoffs but quickly abandoned that idea. It would be just too difficult to set them all to the same extension.

Another spider tip: Measure and memorize the diameter of the central hole in the front of the chuck. Whenever you encounter pipe a bit larger than that size, grab a foot or so for the tool pile. Cut off short lengths to make custom offset spiders as needed for larger diameter jobs.

 

[Peter Neill]

My version uses a height adjustable spinner on a threaded shaft to adjust the offset, so you don't need any other parts, and the only the one 'unit'

Details of it here: http://www.homemodelenginemachinist.com/index.php?topic=3911.msg40481#msg40481

And a more detailed build story over the 'other side' here: http://bbs.homeshopmachinist.net/showthread.php?t=32701

Peter

 

[black85vette]

If you have a small lathe as shown, you may be able to get away with only one spider offset determined by the thickness of the spider body. For larger equipment you may want to make the spider offset adjustable.

Thanks Marv. I am planning on one like yours for my 8" chuck on my big lathe. It is a really useful and simple design.