Tiny set screws on new pinions

[Chuck Keysor]

Hello Shopbot Friends:

In 2017, I bought a full set of 5 new 20 tooth pinions from Shopbot ($125 total). I noticed today that the set screws on the new pinions are really tiny, and neither the metric or English Allen wrenches fit right!

I have a full set of metric and English Allen wrenches. The best fitting English allen wrench measures .091" (3/32), but it is a little bit loose. The best fitting metric Allen wrench measures .096", and I can not even force it in........ close, but not quite...... (Hmmmm, added note, .096" doesn't convert into a nice metric,,,,, so this set screw isn't even even close to a metric size.)

The set screws on my old pinions accept a .125" Allen wrench, and the fit is perfect........

I am afraid to use these new pinions, especially for holding up my 5HP spindle on the Z axis, as even if the Allen wrench fit right, I can't imagine being able to really torque these things on tight. With the loose fit, I think it would be foolish to hope these would be reliably tight. (Especially since getting at this pinion later, is really difficult.)

I have thought of:

1) reusing the best of my old pinions for the Z axis, since I know I can really tighten it and it won't come loose. The best used one is only slightly worn.

2) drilling out the holes on the new pinions and tapping them with 1/4-20 holes. (I have only done tapping of soft steel before, and had good luck..... but are these pinions hardened, such that I might expect to have problems? I'd hate to mess up my expensive pinions.)

3) Other ideas????? And I wondered, why on earth would the new pinions have such tiny set screws,,,,, and why would they not match either metric or English wrenches????? (does someone have an adjustable Allen wrench I can borrow??? :confused:)

Thanks, your input is greatly appreciated! Chuck

[coryatjohn]

>> but are these pinions hardened,

The pinions are softer than the rails. I doubt they are mild steel but certainly not hardened.

[Chuck Keysor]

Thanks,,,,,,,,, I guess the more properly focused question which I should have asked is: With some basic experience in tapping non-hardened steel, can I reasonably hope to drill and re-tap the pinion set screw holes?

[Brady Watson]

With some basic experience in tapping non-hardened steel, can I reasonably hope to drill and re-tap the pinion set screw holes?

Yes...Just do it.

Machine yourself a jig that will hold each pinion in a cradle square to the drill press quill. If you don't have a drill press, find someone who does. Pull the grub screws out of the old pinion, match up the threads, drill and tap the POS pinions SB sent you and tap them using the drill press quill to hold the tap - by hand. Do not 'power tap' them. There's really not much there to tap...it will go quick. Do NOT do 1/4-20.

When you put them on, use LocTite Blue...Crank them on good. SB gives you 3 wrenches on new machines so you practically bend them out of whack. That's how tight to make them...

[Chuck Keysor]

Thank you Brady. I'll match the thread of my old set screws. I do have a good floor standing drill press and a machinist's vise. (Someone gave me the machinist's vice to get rid of it. I have never used it, but will use it now.)

Side note, I welded my gantry with the rectangular steel tubing, and am slowly putting things back together after that. I finally got to the Z axis reassembly when I found this new issue of the tiny set screws.

Thanks again Brady for your guidance, Chuck

[curtiss]

this chart might be handy ... perhaps 1/4 - 28 ??

[Chuck Keysor]

Thank you for the handy chart Curtiss. I'll go out tomorrow and buy a tap, as I don't have the right size in my limited stock. Thanks, Chuck

[Brady Watson]

Get yourself a thread gauge too if you don't already have one in your tap and die kit. Don't expect most big box stores to have taps in stock... that would be too useful...

[coryatjohn]

And... don't waste your money on some no name brand tap. Most likely, it will crack within two turns in steel. Get a Hanson tap. They seem to hold up well.

[jTr]

the POS pinions SB sent you

Sounds like your implying that SB's supplier has changed, or altered quality of pinions...
Are we all expected to go through an hour of re-machining pinions as such going forward, or is this just a fluke?

jeff

[brian.owen]

Those look to be M5 set screws -- 0.96" is a little under 2.5mm -- and a 2.5mm allen key should fit an M5 -- snapping a measurement from the photo you posted seems to agree. I'm not sure why the set screws would have changed from 1/4-20 to M5 -- Although -- I looked up your order from 2017 to get the part number. There is a note on that part that suggests that back in 2012 we had 1/2 pinions bored out to 14mm by our supplier to fit the motors we were using. Since then, it looks like we are purchasing a pinion that comes standard with 14mm bore -- which would likely mean metric set screws. M5 is a fine-thread screw and should be able to take about 5 ftlb of torque vs about 9ftlb for a 1/4-20.

[Chuck Keysor]

Thank you Brian for looking into this. Maybe this sound dumb,,,,,,, while I am no machinist, I do have a couple of complete sets of English and metric Allen wrenches, plus a box full of misc. I didn't find any that fit right........ I found loose fits, and just a bit too big fits..... Where as I have a bunch of 1/8" Allen wrenches. Doesn't an M5 set screw boarder on a specialty size?

I came very close to trying to just tighten these set screws with what I had, as it was late at night and I wasn't thinking well. But then I realized I'd be the one stuck trying to deal with loose set screws. I will drill mine out and end up with a bigger/common sized hole in my pinions.

Thanks, Chuck

[brian.owen]

Chuck,

The M5 x 0.8 is pretty typical in metric stuff -- it is also just about a perfect match to a 10-32 (good thing to remember when you're in a pinch and don't have any metric screws!) -- the socket cap M5 uses a 3mm (almost 1/8") allen -- but the set screw variety uses the 2.5mm (same as the socket cap M4) Most metric allen sets should have a 2.5 so it could be worth another try (maybe some crud on the screw blocking the socket?). Though as others have said--you should have no problem drilling out and re-tapping and M5 hole to 1/4-20 and getting full threads.

Brian

[curtiss]

A "Fine thread tap" is much easier to use for tapping such a shallow hole...

I think I have thrown my 1/4 20 away....

[Chuck Keysor]

Well, as was suggested, it turned out the drilling and tapping of the 4 pinions was not hard. I think I spent a total of 2 hours to do these. But it took 7 days before I started............... I mounted the tap into my drill press chuck, and turned it by hand as Brady suggested. Thanks everyone for your input! Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=32807&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32808&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32809&stc=1

[coryatjohn]

>> I mounted the tap into my drill press chuck, and turned it by hand as Brady suggested.

I never thought of doing that. Missed where Brady recommended that. Great idea. I will keep that in the back of my brain for reference.