Proper Method for Making a Spider ?

Jim Kobe said:
Or...you could just order some brass tipped allen head cap screws from MSC. I ordered the 5/16-18 ones and they work great.

As for fitting the spider, try this. CHuck up a piece of stock large enough to mimic the OD on the spindle (back side) of your lathe. Measure the OD and TPI and go for it. Start the thread and with your dial calipers, measure the pitch diameter of the spindle. This will not be a true Pitch diameter but it will be close. Write it down and keep threading your test piece. When you get it to the pitch diameter of the spindle you are done. Take it out and when making your spider, use the test piece to check the fit on the inside threads. It works, believe me. And you don't sdneed to take it out of the lathe to check the fit or pick up the thread again.

Jim
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Hi Jim,

I have a piece of stock that I cleaned up to do this with.

I defintely believe it works if YOU do it, but the jury is still out with respect to my work.:eek:

Thanks for all the help.

Jim
 
What you are doing is using the caliper only for comparison; take the dimension from one part and transfer to the other. Not rocket science but it works.
 
Jim Kobe said:
What you are doing is using the caliper only for comparison; take the dimension from one part and transfer to the other. Not rocket science but it works.
Click to expand...

Yup, thanks Jim.

Have a slight problem that is holding me back at the moment. Got the gears for the metric thread in last night and tried to cut a thread. Didn't work. Each pass was .002 to .003 past the previous one. I have cut some pretty good looking American threads just fooling around, so I am thinking it has something to do with the leade screw or some combination I don't know about. I am trying to get ahold of Matt at PM to see what he says.

Thanks again Jim.

Jim
 
Jim are you just reversing you lathe at the end of the thread when cutting metric threads or are you disengaging the half nut ?

Hal
 
Hal said:
Jim are you just reversing you lathe at the end of the thread when cutting metric threads or are you disengaging the half nut ?

Hal
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I was disengaging the half nut. After checking everything again (half a dozen times) it was getting late and I couldn't remember the method you guys mentioned of just reversing the lathe, so I didn't get a chance to do try that.

I am going to try to call Matt again soon. I want to know what is going on and if the threads will indeed be the correct size. I am betting I can cut them by leaving the half-nut engaged but don't want to go through all that and then find they aren't the right threads.

Jim
 
I am guessing Hal, you were going to tell me you aren't supposed to disengage the half-nut to cut metric threads.

Just got off the phone with Matt. It will cut the correct thread, just don't disengage the half-nut.

Cool............will be makin' some sulphur smoke tonight.

Jim
 
Bob Pastor said:
Hi Jim,

Here is a video link for re aquiring a thread. http://www.youtube.com/watch?v=FfwdsBYJN34

Just incase you want to make a spider that threads into your outboard spindle, check to see if it's a left hand thread. Since most lathe work is turning forward or towards you, usually the threads on the outboard side are left handed. I found this out the hard way after spending a very long night trying to screw right hand threads into a left hand threaded spindle.

Bob
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Talk about a smoke and mirrors video. If the guy in that video keeps the same zero relationship on the cross slide, i.e. he does not reset the cross feed dial, and then he dials the compound in to get is left/right alignment, he has lost his relationship he had originally between the tool tip and the cross feed dial!!!
 
Hi Jerry,

No smoke and mirrors were used during the filming of that video. It just worked out that I did not have to reset the cross feed dial on that set up. The reason was because I had just finished threading that piece and wanted to show how to re aquire the thread once the piece is removed and put back in the lathe. Sometimes you just get lucky. 99.9% of the time you do have to reset the cross slide after moving the compound to re align the cutting tool. luck happens, sometimes on the range and sometimes on the lathe.

Bob
 
Bob Pastor said:
Hi Jerry,

No smoke and mirrors were used during the filming of that video. It just worked out that I did not have to reset the cross feed dial on that set up. The reason was because I had just finished threading that piece and wanted to show how to re aquire the thread once the piece is removed and put back in the lathe. Sometimes you just get lucky. 99.9% of the time you do have to reset the cross slide after moving the compound to re align the cutting tool. luck happens, sometimes on the range and sometimes on the lathe.

Bob
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My point here is to make novices aware that 99.98% of the time there are other adjustments that HAVE to be made to synchronize the tool with the thread. That video makes it look like the synchronization will be automatic and that misconception could cause the novice to wreck the workpiece or worse the machine!!

You make a deception in saying "The reason was because I had just finished threading..." Not so. The reason was you, as you now admit, were just lucky.

I taught Machine Tool Technology for several years at the junior college level. When dealing with the novice and machine tools that can seriously injure, always show the worst possible scenario not the simplest.

Bob, I'm not trying to be a pain here, I just want viewers to know there is much more to picking up on an existing thread than that video shows. When teaching machine shop at the high school level one has to be careful, when teaching at the junior college level one has to be extremely extra careful since some of this latter class of students have no mechanical aptitude at all. That video is exposed to an even wider audience.
 
Hi Jerry,

For god's sake I just made a very small mistake in not explaining that most times you have to adjust the compound and then reset the cross slide back to zero again. I didn't try to make any kind of deception. The process did and does work. There isn't anything that difficult in the process. Maybe you could help me out by explaining what else is needed to pick up an existing thread. What did I leave out in the video?

As long as the point of the threading tool is lined up with the center of the thread, to be re aquired, what else is there?

Bob
 
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Bob Pastor said:
Hi Jerry,

For god's sake I just made a very small mistake in not explaining that most times you have to adjust the compound and then reset the cross slide back to zero again..... Maybe you could help me out by explaining what else is needed to pick up an existing thread. What did I leave out in the video?

As long as the point of the threading tool is lined up with the center of the thread, to be re aquired, what else is there?

Bob
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The video implies that picking up an existing thread simple and is automatic. It is not. Watching the video, a novice would expect that when you move your cross slide dial to zero, everything would be in sync.

I think it would be helpful to edit the video to show how to sync the tool with the existing thread once the half nut is engaged, don't you. It is your video, it IS helpful, but at the same time it is incomplete in not showing what is involved in that 99.98% of the time that a lateral adjustment has to be made.
 
Due to backlash between the lead screw and the half nut, I have to pick up existing threads while the carriage is moving.
 

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pdhntr said:
Hi Jim,

I have a piece of stock that I cleaned up to do this with.

I defintely believe it works if YOU do it, but the jury is still out with respect to my work.:eek:

Thanks for all the help.

Jim
Click to expand...

Funny thing, when I mentioned this about the brass tipped cap screws I was about to send in an order to MSC and thought I might as well order more of them as the ones I was using were getting kinda flat. Went to the catalog and could not find them; call customer service and was told it was a discontinued item but could be back ordered and "...will call you back..." I got an email the next day from them asking if I still wanted them. Guess what, $286 for 8 cap screw because "...they had to be made special order.."

I will make my own now.

Jim
 
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Jim Kobe said:
Funny thing, when I mentioned this about the brass tipped cap screws I was about to send in an order to MSC and thought I might as well order more of them as the ones I was using were getting kinda flat. Went to the catalog and could not find them; call customer service and was told it was a discontinued item but could be back ordered and "...will call you back..." I got an email the next day from them asking if I still wanted them. Guess what, $286 for 8 cap screw because "...they had to be made special order.."

I will make my own now.

Jim
Click to expand...

Hi Jim,

I just finished the spider last week and it came out better than I expected.

I turned a steel "spud" with the same threads as the spindle, and that came out perfect for checking the threads in the spider, just as you (and others) said. I backed out the lock nut on the spindle and used that to check the spud.

Even though the spud screwed right into the spider (in the chuck) when I did the trial fit on the spindle it was a little too tight. I had to chuck it up again and pick up the thread and take a couple more thousands. The second time it was perfect.

I used 3/8 cap screws and drilled the ends of the screws for aluminum inserts that I turned on the lathe. I expoxied these inserts in.

I polished the spider up 'cause it looked so nice, and several hours later, knocked it off the bench onto the concrete floor. Now I have to do a little more polishing...........but the spud works great for polishing.

All in all, it was more of an educational project than another tool project, and that's what I was after.

Thanks to all that helped. I really appreciate all the information and wisdom.

Jim
 
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