DIYed XL 037 Belt pulleys for the 7 x 14" mini lathe.

[DIYSwede]

CAUTION: Yet another verbose post!

The Chinese 7" Mini Lathe variations have one common issue - non-standard motor drive belts,
which quite a few users (other than me) have found shred easily,
either the motor's plastic or the driven pulley but also the belt itself have had reported quality issues,
apart from it being relatively expensive ($ 25 + S&H), having long delivery times and are sometimes hard to find:



The gear ratio of the original is also sub-optimal for my taste as well:
17 and 31 teeth, giving 1:1,82 ratio and a top rev of 2500 rpm.
This, along with the low torque at low revs isn't very useful to me,
and after seeing some owners successfully installed this conversion kit, I too wanted a 3.1 reduction kit:



Readily available on FleaBay etc, there's only one down side:
The price tag: $ 120 + $ 20 S&H...

I checked quite a few small belt systems that within the lathe's small confines would give:
1) Maximum gear reduction, and thus max torque at any speed for the given motor. 1600 max rpm
2) Being a cheap, readily available and standard belt.

Though there are a couple of belt types that could stand greater force at low revs than the XL type,
I still decided on that type as I already scored a few extra 10T aluminum pulleys (for a buck each)
when I winged this together: DIYSwede's TPMDGM: A Flip-Flop ToolPostMiniDriil/Mill/Grinder for a 7x14" lathe

And when 3 belts of just the right length (210 XL 037) was ordered and delivered at 2 bucks apiece,
I felt I was on the home stretch - just source a Delrin 30T 10 mm wide pulley and smack it in.

Well, this wouldn't fit neither the forum nor the title above - and though readily available just about everywhere,
they were still too un-cheap for my taste, so I thought of "just winging one together"... (Famous last words!)
This is where the fun starts: Milling a 30 tooth XL pulley in the aforementioned 7 x 14" mini lathe:

Having found some 17 kg of 1/2 & 3/4" Delrin offcuts and finding that the OD of the pulley should be 48 mm,
cut a 50 mm square piece of 1/2" thick Delrin to fit. Also having plenty of cast iron waste around,
I thought I'd make a spare if the plastic gear wouldn't stand up to my intended use.



Turning, drilling and boring the two piece's holes 10 mm was simple, then broaching a 4 mm keyway in the plastic was quick ,
but somewhat tedious with the CI, giving me a blister from the monotonous handwheel feeding:



I turned a 10 mm mandrel and fit the Delrin: easy, clean turning but with helluva swarf,
where cast iron is fine and dirty, as usual:



Using my TPMDGM I figured I'd need to turn, grind, harden (no tempering) and lap a piece of 4 mm drill rod D-Bit to suit this:

-Here we go - everything fitted, trued, and indicated for 50 thou DOC, using the Indexer for the 7 x 14" mini lathe
to achieve the intended 30 tooth division:



Plastic went just fine in one to & fro pass by the electric lead screw at 30 mm/min and 2 k rpm,
while the cast iron needed an extra spring pass to get down to shape.
Could run the mill wide open for about 5 minutes before having to let it cool down,
as the ex-furniture motor only has a 20% duty factor...
Belt test fit showed that the rounding of the crests really was necessary, so I chucked a 1/4" ball endmill,
and gave them both a slight kiss to achieve a nice fit:



Then finally only a facing down to 10 mm thickness was needed- taking off 50 thou on each side and finish off to fit:



Thanks for following me this far, questions welcome!

Fitting and adjustments in the lathe will commence tomorrow...

Cheers

Johan

[Crusty]

I made the XL pulleys for my mill when I upgraded the motor and they were easy to make on my milling machine with a rotary table. I ground a cutter bit for a boring bar to the tooth profile and away I went. My pulleys didn't have flanges so I made some washer type flanges and shaft collars to lock them onto the shaft and it all worked out as I planned and they're still operating with no problems today. I think XL drive systems are great because they inexpensively solve a variety of drive and speed reduction challenges and are quite durable.

Be careful buying pulleys though - the XL pulleys for 3D printers don't have the same pitch as standard XL pulleys.

[DIYer]

Thanks DIYSwede! We've added your Mini Lathe Pulleys to our Lathes category,
as well as to your builder page: DIYSwede's Homemade Tools. Your receipt:

Mini Lathe Pulleys by DIYSwede

tags: lathe, pulley

[DIYSwede]

Well - started out this morning with the belt - pulley conversion - nothing dramatic:



Tore the old stuff away, suddenly realizing the length discrepancies between the new and old belt:



A new run of the old belt length formula:

Lp= Pitch length, A= Axle c-c (108 mm), Do= Large pulley pitch dia (48,5 mm), do= Small pulley pitch dia (16,17 mm)

Gave the value: 317 mm, which correponds to a 126 XL 037 belt (63 teeth)
(not a 210 XL, which I wrongly ordered 2 years ago).

Just happily placed another $13.50 order (incl free shipping) for 3 belts,
with the absolutly reasonable delivery window from 3 weeks 'til the end of May...''
That money can in three days get me one belt of the very same brand thru a national distributor, so I guess I'll just sit it out?
The same company would also kindly offer an aluminum 30T XL pulley (w/o flanges) for 55 bucks...
i.e. a 10 mm offcut from a 30T solid extrusion. Bargain!

Goes to show that I shouldn't have been so cock-sure when ordering the previous ones?
The Dunning-Kruger Effect still hits me hard from time to time, as we're all confident idiots at times.

My late grand-dad once told me in the wood shop: -"Measure 3 times, so you'll only need to cut once."

So - this project is temporarily on hold, "due to unforeseen human error"...

[DIYSwede]

-Awaiting the proper drive belts, guess I won't sit on my hands?

Chucking the new 10 T motor pulley, I had to take it's center hole up to 8 mm ID
with a 3 mm keyway (original 17 T plastic pulley had a key already molded in).
After drilling out to 7 mm, sneaking up to 8 with a carbide mini boring bar, 1 k rpm and slow (30 mm/min) feed:



Didn't particularly desire to file the entire 3 mm keyway, I thought I'd use the TPMDGM to start the keyway, at least:



Did a crude sketch to find the max angle for the mill's 4 mm shank to NOT rub on the hole:
12 degrees, with max 16 deg at the full 1,5 mm DOC.

For holding the chuck absolutely still (realized when milling some tool steel the other day) the indexer only wasn't up to the job,
so I kludged a chuck clamp together from an old, salvaged cine zoom lens holder:
The Cooke Super Cine Varotal 25-250mm f/2.8* (where my holder don't have the "Fluidrive" bulge, as seen at far right):



The holder has a positive 100 mm ID hold, without turning when tightening up,
and with a little hardware (a 38mm cylinder and some feeler gages) on the spindle housing to wedge it
for the extreme duress the TPMDGM puts the headstock thru:



Final results, with only minimal adjustment/ filing needed:



Thanks for reading - hope you found something useful/ entertaining! Questions & comments always welcome!
Cheers
Johan

* Though "State of the Art" in the eighties, today considered "vintage"- it can now be bought on Ebay for 3- 5.5 k$,
or had from Cine Rental companies for a mere $ 250/ day...

[DIYSwede]

Belts arrived, mounted and taken for a 30 min spin w/o odd results, belt climbing or weird noise:



Seems good enough to get the whole shebang remounted.
Expenditures: 25 bucks, and app 8 hrs of work, tops.

Cheers,
Johan