Need help with lathe spider

C

chuck williams

Guest
i am in the process of building a spider for my lathe. i have the interior and exterior dimensions now but i need to drill and tap the set screws. how do i index the spider to 90 degrees without an indexing head or other specialized equipment? i have the circumference. can i just divide this by four and drill by eye and be close enough? also, what size drill bit do i need to use for 1/4" and 3/8" set screws? need help asap. i hope to finish this today. thanks, and MERRY CHRISTMAS!

chuck
 
Chuck, I will let someone else answer the indexing question, but I would like to make a suggestion. Use the finest thread screws you can find. A nudge on a fine thread will move the barrel less than a nudge on a course thread. This is helpful when you get down under a .001". Also with a fine thread you don,t need a locking nut as the ramp angle is flat enough that the screw won't back off.

I used a 1/4" - 28 X 1". I found them at McMaster Carr with a brass tip. For a 1/4" - 28 you need a #3 drill.

Dave
 
thanks dave,

i will be using 1/4x20 for the set screws between the spider and spindle and 3/8x24 for the adjustment screws.

chuck
 
3/8 24 will be a Q drill and the 1/4 20 will be a #7 drill.

To drill the adjusting holes on mine I set the spider on end and milled a small flat. Then turned it over and milled another small flat. At that point I had 2 flats 180 degrees from each other. Then I put it in the mill vice flat (laying down) clamping on the flats and milled the other two flats with the side of the mill. I then had four flats, one at each 90 degrees. Then I set it back on end found the center by sweeping it in with an indicator and drilled each hole one flat at a time.

Dave
 
dave,

i never though of that. it would certainly work. hoping for another option, but if not, i may just do that. thanks again.

chuck
 
Indexing 90 degrees

Why not put it in the four jaw chuck and scribe a line at each jaw?
 
The four jaw chuck idea is fine, but as a general comment. For the accuracy required in a spider, layout dye and a scribe/machinist rule and square dial calipers etc, and you can lay this out. Like any shop project. Machine tool fundementals.
 
jwa said:
Why not put it in the four jaw chuck and scribe a line at each jaw?
Click to expand...

That'll work. It doesn't need to be very precise.

When I made my receiver truing sleeves I put it in a 4J, use a small level to set the jaw vertical or horizontal, which ever is easier, then scribe down the length of it with a turning tool using the carriage. rotate it till the next jaw is in position, scribe again. Repeat 2 more times and you have 4 lines at close enough to 90 degrees apart that the difference won't matter for a lathe spider.

I made some 1/2-20 centering bolts with brass ends out of hex stock I had lying around.

Fitch
 

Attachments

  • Done - from outside.jpg
    Done - from outside.jpg
    35.8 KB · Views: 2,918
  • Cathead parts - 1.jpg
    Cathead parts - 1.jpg
    21.9 KB · Views: 1,730
thanks for everyones help. i got it done today in the mill. i took the circuference divided it by four and made marks on a piece of paper i wrapped around the spider. i scribed at those marks. in the mill, i used a straight edge to make sure i was drilling straight through to the center of the spider. it is not perfect but it works very well. i have a barrel in it right now. it works perfectly. thanks again.

chuck
 
You must log in or register to reply here.
Back
Top