New cross slide screw and Delrin nut for Rivertt 1020S - Page 2
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  1. #21
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    Quote Originally Posted by Cole2534 View Post
    I don't want moglice, nor is it an option. The nut in question is 2.4" long and I don't have 2.4" of virgin thread to model from.

    I want bronze, but for the cost of admission and learning potential I'm going to use delrin.

    Sent from my SM-G930R4 using Tapatalk
    Just for clarification you don't have to use virgin threads, just use the section of the screw with the widest threads. Reason bring, if you mold the epoxy around the thin areas it'll jam up over the relatively unworn areas.

    Sent from my XT1053 using Tapatalk

  2. #22
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    Today I made the tap. Lotta firsts in this one so I'm open to critique. The OD is 0.0025" over the major diameter. Unfortunately I couldn't get a good measurement over the wires so I'm not positive the form is perfect. I think it will perform well for my purpose of tapping Delrin, just gotta make the screw to fit.

    Sent from my SM-G930R4 using Tapatalk

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  4. #23
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    Quote Originally Posted by Cole2534 View Post
    I don't want moglice, nor is it an option. The nut in question is 2.4" long and I don't have 2.4" of virgin thread to model from.

    I want bronze, but for the cost of admission and learning potential I'm going to use delrin.

    Sent from my SM-G930R4 using Tapatalk
    Sorry - but THAT is bass-ackwards.

    The screw... always wears more in one spot than others.

    The nut ... never does.

    You'd have better consistency to retain the worn Bronze nut and replace the SCREW.
    THEN you could Moglice the nut. For the work and cost involved? I'd not bother.

    Delrin can't fix uneven wear in the screw.

    Neoprene, maybe?


  5. #24
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    Quote Originally Posted by Monarchist View Post
    Sorry - but THAT is bass-ackwards.

    The screw... always wears more in one spot than others.

    The nut ... never does.

    You'd have better consistency to retain the worn Bronze nut and replace the SCREW.
    THEN you could Moglice the nut. For the work and cost involved? I'd not bother.

    Delrin can't fix uneven wear in the screw.

    Neoprene, maybe?

    Just what the #### are you talking about?

    I made the tap because it's a small section of screw that I could gage to my liking. Next I'll thread/finish the nut. Third operation is to cut a new screw using the nut as a gage. If all that goes to plan, I'll install the combo in the machine. Or not.

    Sent from my SM-G930R4 using Tapatalk
    Last edited by Cal Haines; 09-05-2017 at 04:41 PM. Reason: profanity

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  7. #25
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    Quote Originally Posted by Cole2534 View Post
    Just what the #### are you talking about?

    I made the tap because it's a small section of screw that I could gage to my liking. Next I'll thread/finish the nut. Third operation is to cut a new screw using the nut as a gage. If all that goes to plan, I'll install the combo in the machine. Or not.

    Sent from my SM-G930R4 using Tapatalk
    Seems it is ALL going clear over your head, so never mind... carry on as you are.
    Last edited by Cal Haines; 09-05-2017 at 04:41 PM. Reason: profanity

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    Cole

    Let us know how it works .

    Hal

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    I would single point cut your nut slightly undersize first then use your tap. Your tap doesn't have a long enough tapered lead it might not make a clean cut. Small bites tend to make a cleaner cut less tearing. You can always try it then make changes to it if necessary

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  11. #28
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    Quote Originally Posted by vettebob View Post
    I would single point cut your nut slightly undersize first then use your tap. Your tap doesn't have a long enough tapered lead it might not make a clean cut. Small bites tend to make a cleaner cut less tearing. You can always try it then make changes to it if necessary
    That's a great idea, thanks. AS far as the taper, in hindsight I can see that it may need more. That's OK, I intend to add more relief as well for chip evacuation.

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    Guys, Please keep your post courteous and avoid using profanity.

    Thanks.

    Cal

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  14. #30
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    Did you add periphery relief (I guess that's what it's called) to the teeth of the tap? If so, did you use a relieving attachment? If not, did it work fine without it?

    Sent from my XT1053 using Tapatalk

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    Quote Originally Posted by Spyderedge View Post
    Did you add periphery relief (I guess that's what it's called) to the teeth of the tap? If so, did you use a relieving attachment? If not, did it work fine without it?

    Sent from my XT1053 using Tapatalk
    I didn't, but I thought about it. I don't have a relieving attachment so my plan was to set the tap in my indexing head eccentrically and rotate the piece into the cutter.

    I made the nut this weekend, but didn't take pics. doh. I did remember to measure the backlash on my existing screw, 0.090".

    The tap worked pretty well. I had to add more relief, as I suspected, and if I had it to do again I'd have made it a very long taper. Typical plug taper (3-4 threads) wasn't gradual enough to cut the threads in a single pass without pecking. I had a feeling that was the case, but decided to try it anyway. My plastic nut would only thread onto the factory (I think) screw about 3 turns before it got very tight. All of the clearances and pitch are correct, so I can only figure that the error is somewhere in the included angle of the thread flanks. However, I'll be cutting the screw with the same tool I cut the tap with so that error should cancel. Knowing all of this now, I'd skip the tap and single point the threads. I initially discarded that idea because I didn't think I had proper equipment to make a single point threading tool capable of cutting this thread. I now know that Fatigueproof (what I made the tap from) is plenty capable of this duty and readily machined.

    As far as the plastic nut's strength- I was concerned about forces during knurling but it occurred to me that the limiting factor is the strength of the screw at the taper attachment bearing block where the screw necks to 3/8-24. That section should part at about 1/5 of the nut's pullout load, given a Stressproof screw.

    It will be about 2 weeks before I can get back to this project, I'll post updates then.

  16. #32
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    I believe the issue with your but binding was because the plastic deformed during cutting and sprung back causing essentially a smaller thread. When tapping plastics I've heard that you can shim one side of a tap using paper, so only one side cuts and it cuts a slightly bigger thread, so once the plastic springs back it's on size. I do not know if this is true however, I've never had to try it.

    Sent from my XT1053 using Tapatalk

  17. #33
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    Well here's the screw and nut just before I drilled the cotter pin hole and milled the taper attachment slot. It wired 0.002 under perfect per my pee dee chart and when I did a quick check on the mill the pitch error was about 0.001"/in. There is no lash between the two that i can detect by hand.

    On another note, this was the first long-ish shaft I've cut in that machine and it was a straight cutter. The screw tapered down toward the headstock so I'm hoping I can dial that out with the tailstock.

    Edited for clarity
    Last edited by Cole2534; 09-14-2017 at 07:39 AM.

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  19. #34
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    Quote Originally Posted by Cole2534 View Post
    On another note, this was the first long-ish shaft I've cut in that machine and it was a straight cutter. The screw tapered down toward the headstock so I'm hoping I can dial that out with the tailstock.
    That ends up pretty hit-or-miss because the amount of flex depends on the cutting pressure and that depends on depth of cut, speed, tool sharpness, etc. The best option on something bendy like that is to use a follow rest backing the tool.

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  21. #35
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    Quote Originally Posted by rke[pler View Post
    That ends up pretty hit-or-miss because the amount of flex depends on the cutting pressure and that depends on depth of cut, speed, tool sharpness, etc. The best option on something bendy like that is to use a follow rest backing the tool.
    Unfortunately, I don't have either rest for this machine. Bu I do have a large heavy steel ring that I intend to repurpose.

    Sent from my SM-G930R4 using Tapatalk


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