Source for 1.375 x 24tpi EXTERNALLY threaded tube/pipe?

[Qwiksand]

With my kona mid-drive, I'm in need of a 40-50mm long tube or pipe with standard 1.375 x 24tpi right hand threads on the outside- ideally it would have 26 or 30mm inside diameter so I can run standard sizes of sealed bearings as well, but this is less important as I can print bearing shims.

Essentially, I'm in search of an extra-long left hand sided bottom bracket cup. Has anyone seen anything like this on the interwebs? I may try ordering a large die and making one or, if that fails, I'll resort to a machine shop.

 

[NeilP]

Funny you should ask this..I was just about to spin up a mates lathe in the next few weeks to make some myself.

If you find a source, post back here..it will save me a job.


Though from what I have seen on here with regard to getting stuff machined in USA, from people that have had chain rings cut, you will probably be just as cheap getting some machined at a local machining shop.

I did some passes on the lathe the other day, but forgot what I was doing and then cut a LH thread across the top of the RH thread... has been 20 years since I did any thread cutting, and even then , it was only one big internal thread...2 TPI /..not as fine as 24tpi.

 

[yawstick]

I just made something similar on my lathe. It is an adapter to mount a BMX freewheel onto a shaft to drive left side of the rear wheel of a recumbent trike. I'm not sure and want to order a bottom bracket shell to test with (to test on the lathe if I decide to make something to fit it) but I've noticed they have 1.37 x 24 as the stated size and my adapter wont screw into the bottom bracket shell on my trike.... and it does fit the BMX freewheel which is 1.375 x 24. Wondering if the .005 missing from the shell is an english thing and why it wont fit. I'm thinking of using the shell on my recumbent to mount a jack shaft to drive left side of rear wheel.

Pics here may help although the friction drive is temporary. http://electricktrike.blogspot.com/

 

[NeilP]

Is it something obvious but overlooked?

Like you cut a conventional right hand thread on the adapter and the freewheel is left hand thread?

How many passes did you use to cut the thread? P

 

[yawstick]

A little background... I'm a long time maintenance type with strong electronics background... have spent a lot of time in machine shops at various places I've worked. Lucky enough to have a lathe and milling machine at home but only recently undertook thread cutting on the lathe.

The adapter does fit the freewheel which is 1.375 x 24 rh ... it will start into BB shell but tight and have not tried to force it. I was looking at BB at a cycle shop and noticed it only says 1.37 x 24 so I'm thinking it an off standard from way back and too small for the adapter threaded for 1.375.

I made multiple passes when threading this part and had a freewheel in hand to try it as I went... when I was close I began on taking a few thousandths each pass til the freewheel would go on easily.

I was pleased with how this went and wanted a smaller tooth freewheel as 16 tooth is as small as you can get with the 1.375. Smaller ones are metric 30 mm OD by 1mm thread. My lathe will not cut metric threads so I decided to try the shadetree universal thread. 1mm thread is 25.4 threads per inch so I cut 26 TPI on a 30 mm shaft. I followed the same technique with freewheel in hand and continued to take off material until the freewheel would go on easily.

Surprisingly it worked purty dam good.... my intials by the way PDG.

I've added some more pics of them at http://electricktrike.blogspot.com/

 

[NeilP]

neat solution..like it.

I am laid up at moment, broken arm in August folowed by tendon graft last month, so no time to get on with my work

Like the knurled drive for the friction drive much better than the sticky emery tape method over the motor!

 

[solar.g]

According to Sheldon Brown's website (http://sheldonbrown.com/freewheels.html), and others, there are subtle differences between 1.375", 1.37", English/French/Italian 24TPI threads.
Angle of cut and a few thou difference can make one easier or harder to screw on (or impossible to screw off).
I had a machine shop make me a custom freewheel/sprocket adapter (for a Cyclone mid-drive installation on a recumbent trike) and took a selection of sprockets and freewheels to the shop to have them confirm that the thing they made me would fit my freewheels/sprockets (White ENO FW and Surly sprocket, in the end).
I think they might have erred on the side of sloppy, but the thing works, so ....
The point is, take the devices you wish to spin onto your tube/shaft and check it works.
If a bit tight you might be able to get away with some Loctite anti-sieze to help it get on/off.
BTW, I couldn't find anyone who sold what you're after, ready-made, on the interweb.
I had to get it custom-made (at great expense, I might add).

 

[yawstick]

Sorry about your bad luck NielP.... best wishes for a speedy recovery.

Just taking the shell / freewheel differences at face value it would appear there is a 5 thousandths difference on their size... more than enough to be a no go. Only a couple of thousandths made a huge difference in putting the freewheel on my adapter.

I ordered a few BB shells to have on hand for testing... also ordered a tandem BB shell with eccentric adjustment... it was from the same site and looked to handy to pass up. Will be experimenting with these in the near future.

 

[NeilP]

thanks

did you grind your own cutting tool for the thread or buy one of the correct angle?

I have bee thinking to use a 'blade' style off cut tool. Can just grind a single flat off the square tip.

and what about angle of the top slide on the saddle..30 degrees right?

Apart from the experimental thread cutting the other day, the last threads I cut was 20 years ago..and that was a lot bigger..about 2 TPI..square section ACME threads..this is a different ball game altogether.

I made a reasonable job initially on my last attempt...grinding and then cutting..then i did something stupid..decided to run the tool back wards along the cut rather than wind it out....doh...just by reversing the feed direction...so thereby cutting a LH thread across the nice RH thread!!

 

[yawstick]

The lathe I have was somewhat inherited and I collected various bits of tooling along the way. I had a tool steel cutting tool that was already ground to a 60 degree point that I used on the first freewheel adapter and I bought a carbide tipped tool with a 60 degree angle that I used on the metric one and any more that I do. I did a little research online and found some articles about cutting threads... one of them did optionally suggest setting and using the compound slide at something like 29.5 or something (don't quote me on that) and advancing the feed (depth of cut) on the compound rather than the normal place. The theory being you're only cutting one side of the thread as you feed in. I did set the compound angle but I did not use it like that. I did cut practice threads on several thing before my actual part. Sometimes moving the part between passes and was cutting 11tpi. I did find the compound useful for getting the tool back on the correct path by adjusting the compound after engaging the threading feed. That would be difficult on 24 tpi and my description may not be so easy to follow. I'm mostly a wanna be machinist and we're probably way off thread here... pardon the pun.

 

[NeilP]

I did a little research online and found some articles about cutting threads... one of them did optionally suggest setting and using the compound slide at something like 29.5 or something (don't quote me on that) and advancing the feed (depth of cut) on the compound rather than the normal place.

Yes, i guess we read the same article, slightly off from the 30 in order to give hat fractional clearance as you advance the compound

I'm mostly a wanna be machinist and we're probably way off thread here... pardon the pun.

same here.

I have a lathe I use..a biggie...Colchester mascot / Master? ...gap bed lathe, ..72 inch bed...can turn stuff up to about 3 foot diameter with bed section removed..metric and imperial threads
.

if you are not easily upset and have a strong stomach..follow this link. it will really bring home how dangerous these bits of kit can be...scared the s**t outta me

http://www.liveleak.com/view?i=de2_1326399606