Author Topic: Can't find a 3/4-16 female adapter.  (Read 677 times)

Offline RichardDepetris

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Can't find a 3/4-16 female adapter.
« on: November 20, 2016, 03:03:33 PM »
 I have a cheap Harbor Freight lathe I acquired as parts. I don't have a motor for it, but I do have a 1 HP treadmill motor I would like to use. The motor is supposed to be face mounted to a pivoting bracket located under the headstock. Unfortunately, my treadmill motor isn't designed for face mounting.  There no good way to mount my motor in the same location due to its weight and size.

I plan to mount the motor externally by attaching a pulley to the rear end of the spindle.  The problem is that it is 3/4"-16 left male threaded. I can't find any adapters to mount my pulley unless I have it custom made.  I could mount a pulley with a 3/4" bore, but I don't have one and I don't want to marr the threads. Ideally, I am looking for a stud with a female on one end a 20mm straight shank on the other. Finding any parts for adapting metric to imperial and vise versa is extremely hard. I am now willing to use another pulley and it has also proven to be equally difficult.

This search has been one of the most frustrating experiences and makes me want to invest in a metal lathe. Why are such parts hard to find? The closest thing I can find is a tube welding bung, but the outer diameter on the smallest end is 1 1/8".  A compatible pulley would be too large and expensive. Any ideas of where to look?  All of my usual suspects, ebay, amazon and even McMaster Carr have come up short. 


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Offline DavidA

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Re: Can't find a 3/4-16 female adapter.
« Reply #1 on: November 20, 2016, 03:43:02 PM »
Richard,

A photo would probably help clarify things.

But isn't there some way you can bodge something together with string and sealing wax that will allow you to run the lathe to make it's own adapter ?

Dave.

Offline chipenter

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Re: Can't find a 3/4-16 female adapter.
« Reply #2 on: November 21, 2016, 08:59:50 AM »
Have you looked for a left hand 3/4 AF tap or die ?
Jeff

Offline Lew_Merrick_PE

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Re: Can't find a 3/4-16 female adapter.
« Reply #3 on: November 21, 2016, 11:39:39 AM »
Richard,

The tap drill for a .7500-16UNF thread (LH or RH) is 11/16'ths (.6875) inch.  A pulley with a bore that size (or smaller) should be fairly easy to thread as .7500-16UNF-LH -- either with a tap or on a lathe.  Not knowing where you are located makes it hard for anybody here to offer you assistance.  [That's located in your user settings.]

Offline Baron

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Re: Can't find a 3/4-16 female adapter.
« Reply #4 on: November 21, 2016, 11:42:20 AM »
Hi Richard,

Not quite what you were looking for but might help.

http://www.clipsandfasteners.com/Inner_Standard_Cap_Nut_Left_Hand_Thread_p/a12520.htm

Best Regards:
                     Baron

Offline jcs0001

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Re: Can't find a 3/4-16 female adapter.
« Reply #5 on: November 21, 2016, 04:44:16 PM »
Richard:

It's easy for me to an "armchair machinist" but here are a couple of ideas :wave:

One option would be to form a delrin nut/collar over the existing threads, use the motor itself and files or cutters to turn the outside of the delrin nut cylindrical (in place) to the size needed for the inside diameter of your pulley.  Leave one end solid.
You will need a drill press or drill and hand tools for this.

A problem may be the heat and the nearby bearings of your motor - not sure if you could shield these.   More info on using delrin/acetal to form nuts on existing male threads:

http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way

Also I suspect your lathe has the ability to do left hand threads - most of the mini lathes do.  If enough of the parts are intact, you can turn the spindle by hand (make a "jury rigged" handle for the outside end) to form threads on the inside of the pulley or on one end of a sleeve.

John.

Offline sparky961

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Re: Can't find a 3/4-16 female adapter.
« Reply #6 on: November 21, 2016, 09:28:53 PM »
I plan to mount the motor externally by attaching a pulley to the rear end of the spindle.  The problem is that it is 3/4"-16 left male threaded.

Now, I don't have a mini lathe so I can't say for sure, but I wonder exactly what we're trying to rig up here.  I'm picturing that there's a threaded part of the spindle (or one of the gears/pulleys in the drivetrain) that the OP wants to make a threaded adapter for.  This adapter would take a pulley that would then be driven by the treadmill motor.

So.... what happens when you reverse the motor direction?  I see no mention of pins, grub screws, or keys here.  Also, correct me if I'm wrong here but I doubt that threads are intended to take loads in this manner.

I'm very suspicious that the OP is trying to take what they think is the "easy" way, but perhaps isn't actually the easiest or the best way to do it.  It could even be rather unsafe, dare I say it.  However, until I see some pictures it's really just speculation.

Offline RichardDepetris

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Re: Can't find a 3/4-16 female adapter.
« Reply #7 on: November 27, 2016, 09:09:22 AM »
Thank you guys for all the help.  Coincidentally, I already purchased the cap nut that Baron suggested before I posted.  It is a workable solution, but less than ideal. I put the question out there to see if there was a better option.

After your replies, I decided to stop the self-obstruction and just do it. I have a few bad habits I need to break. First, I tend to look for an ideal solution and dismiss ones that would suffice. Second, I fear failure and frustration to the point of complete paralysis.  Finally, this fear prevents me from working with the tools and materials I have until I get better stuff.

I am in the process of putting together a build writeup for this lathe project.  I will have lots of photos and detail as much as I can. I will post them in the appropriate forum when I'm done and will alert you when it's up. 

Again, thanks.