Monday, December 5, 2016

Monday, Monday

Not so much a bad Monday, but an unusual Monday.  Let me recap a little. 

I wrote last Tuesday about finding issues with my Sherline CNC system losing motion on its X-axis.  I ordered replacement parts from an online seller I've bought from in the past: two of the couplers, two of the preload nuts, and two packs of two of the 5-40 screws, on Wednesday.  Those parts arrived on Friday and the company royally screwed up the order.  I received four of the couplers instead of two, none of the preload nuts, and one of the packets of 5-40 screws instead of two.  Contacted the company.  "No problem, we'll fix it".  The replacement parts arrived today, and once again, they completely screwed up the order.  This time I received another two couplers, none of the preload nuts, and one single 5-40 screw.  I'm at a loss for what to do here.  I have six couplers (I needed one, but ordered two), no pre-load nuts and three 5-40 screws. 

Before that, I took some photos of the way the leadscrew and 5-40 screws appeared damaged.  The leadscrew's end, before:
and the 5-40:
I ran a die over the 1/4-20 threads and they look much better.  A new nut from the hardware parts box fits much better than before.  I don't have a die for the 5-40 threads, and the screws are cheap enough that I figured I could buy some easily enough, since I needed to order those other parts. 

Meanwhile, over the weekend, I broke out my Hornady ultrasonic cleaner to clean both the existing pre-load nut and the end of the leadscrew.  It was sounding like things were rattling too much, so I put in a bag of .223 brass that needed cleaning.  After a couple of long soaks, I took them both out.  The pre-load nut was clean even in the tight internal corners.  I ran a toothpick into the leadscrew and pulled out some black goop - probably old grease.  Did that a few times.

I received the 5-40 tap I ordered last weekend on Saturday and immediately put it to use.  It only had to cut a little at the very start of the threads, but then screwed in easily over the full length.  It also pulled out some more grease with metal flakes when I removed it, so I did that a few more times until it came out clean.  Now, one of the two new 5-40 screws fits like it should. 

At this point, I'd think I could assemble the whole thing and try to find if I fixed my X-axis, but I'd still like those pre-load nuts.  The difference between a pre-load nut and a standard issue 1/4-20 hardware store nut is that one face is milled flat and then recessed for the diameter of the end of the coupler to fit into the nut, to maybe 0.1" deep.   


  1. I hate it when a vendor messes up an order.

    And I think I'd start to hate the vendor if they did it twice on the same order!

  2. I just looked at the pictures again, and I noticed the top one is *not* a standard thread.

    Looks more like an Acme thread than any other.

    1. They do look like Acme threads, but another picture I took shows that the threads aren't as square as they would be if they were Acme threads. They just got rolled over.

      One of my problems was that the pre-load nut didn't move properly on the screw threads. I needed a wrench when I should have been able to just spin the nut. A 1/4-20 stainless nut out of my parts bin didn't work right either. After running the die over it, both nuts turn freely.

    2. That's strange, as Acme threads are what's generally used on lad screws.....

  3. The left end (shoulder) of the lead screw looks messed up?

    If in fact the taper is the connection to the motor drive, any bad threads could keep it from being pulled up tight, and certainly a 5-40 is not the sort of thread to put much torque on...

    1. The left end is kind of boogered, but it's never used. The nut for this leadscrew is on the other end of the cross slide, and that end never gets closer than about 3 inches from being used. It doesn't even have to be threaded.

      As for the taper on the right end being useful, I'm with you. When I looked at that, I thought "this needs a key". OTOH, the other two axes still work without losing motion and they look just like this.

  4. Out of curiosity, what is the leadscrew diameter itself?

    It is a bit unusual the screw threads you are dealing with are National, I would have expected metric.

    1. These are Kerk leadscrews, 4 tpi (.250 lead) dual start threads. They're ~.442 across the tops of threads, which look like real acme profile, and are what Kerk calls their 7/16" or 11mm screws, in Kerkote, a permanently self-lubricating coating.

      In '07, I replaced the X/Y axis of my original Sherline mill with this setup. The X-axis gives 18 inches of travel and the Y axis is 12. The headstock doesn't reach to the middle of that; it's still only about 3". The real attraction was the ability to work on larger pieces, even if it took a few setups, like when I cut and drilled the front and back panels on my motor controller box. Another selling point was that they're supposed to be zero backlash and really fast on rapids. One out of two. They're NOT zero backlash, but they can do 90 IPM, and that's handy at times. The Sherline motor is 90W, 1/8HP, so no matter what else you do to it, it's going to be a light duty machine.

      I don't know if that 1/4-20 portion was machined onto the end by the vendor (A2ZCNC, who is now gone), or if the screws were ordered from Kerk that way. Looking at the current Kerk website (Haydon Kerk Motion Products), they're very configurable. When things were looking a little bleak, I was considering emailing Kerk to see if I could get replacements.