Mini Lathe Gets a Drive Belt Replacement...3VX belt and pulleys

[jjr2001]

Long over due but necessary with the new 1HP motor and VFD combo on my mini lathe.
The little 1.5mm pitch timing belt and pulleys would slip and rip out teeth on even small jobs.

First picture shows the new belt/pulleys.
Second picture is the original timing belt and pulleys. The original timing pulley was
about .420 thick and I had to make the new pulleys thicker in order to fit the wider
3vx belt and still leave a bit of material on the side of the new pulleys.

I thought the extreme belt tension that I had put on the timing belt would help but even with
only drawing 2.3 amps (about 500 watts) that darn belt/pulley combo would self destruct.

The first belt I was going to use was a 3L series by 20 inches long. But then I saw the HP
specs for the belt and that was just tool low at low rpm with the small drive pulley on the
mini lathe.

3VX210......Then I found the 3VX cogged belt. HP was more than enough for my use. Both the
3vx and 3L series belts use a 40 degree pulley. The old cog belt and pulley system were put
back in use for the last time. I made two pulleys and added an extra idler to my drive system
so I could use the 3VX210 belts. I found a source for the belts on eBay for a good price and bought
2 of them. (I like spares). This belt is a bit on the long side for the mini lathe so I designed my pulleys
to be quite large. As large as I could fit in the lathe without major work. The design required a recess to
be milled in the threading gear/lead screw direction casting. No problem since I had a 6" rotary table and
a mini mill.

Two pulleys were turned. Spindle pulley is .525" thick and 2.520 inches in diameter. Drive pulley is
.520 thick and 1.980 in diameter. Both of course were cut with a 40 degree taper. (20 deg per side).

Since the belt is so long I had to add a second idler to keep the belt from rubbing on the threading gear casting.
There is not a lot of tension on the new 3vx210 belt but enough to keep it from slipping. Much less tension
than I had to use with the original timing belt.

Minimum speed on the VFD was reduced to 4HZ from 6HZ to get back my very low speed on the spindle since I
made the drive pulley larger than the original. (Got an increase in top speed but not too much higher).
Cruised through the crust of some hot rolled steel like butter with a carbide bit.
Made a few more cuts with the carbide bit and put the new motor/vfd to it's first test over 4 amps.
Yep you guessed it. The new belt performed without any screech,squeal,or slip.
Almost a full KW and it just keeps on turning...Very happy with the new belt/pulley combo.
I ran another test as slow speed and I was able to stop the chuck without any slippage.
The motor current went up and the VFD tripped out. Perfect....

Note two links for the belt. Two weeks ago the smallest 3VX I could find was the 210 or 21 inches long.
Recently I found the 205 or 21.5 inch belt. Originally I wanted a 200 and still can't find one! Anyway I think
you can use belts from 20 to 21 inches long and still fit it all in the space that is available. Pulley diameters
will change if you change belt lengths.

Links:
Belts
https://www.ebay.com/itm/D-D-PowerDr...72.m2749.l2649

https://www.ebay.com/itm/D-D-PowerDr...72.m2749.l2649

Previous thread on Motor/VFD upgrade:
http://www.homemadetools.net/forum/n...060#post120414

Previous thread on first idler bearings for the old timing belt system:
http://www.homemadetools.net/forum/m...175#post121106

[olderdan]

Nice work as usual and a and a good use of idler pulleys to get around an obstacle, only served to increase the grip radius on the small pulley.

[jjr2001]

Thanks Dan, the lathe is a joy to use now!
Cheers, JR

[DIYer]

Thanks jjr2001! We've added your Mini Lathe Pulley Modification to our Lathes category,
as well as to your builder page: jjr2001's Homemade Tools. Your receipt:

Mini Lathe Pulley Modification by jjr2001

tags: lathe, pulley, motor

[wizard69]

Nice work! I'm glad you pointed out that a belts horsepower rating varies a lot with RPM and pulley size. I've seen a lot of undersized belts over the years and a lot of the Chinese equipment are good examples of bad belt selection.

Now that you have a proper belt, you will have to worry about breaking something else on the machine.

[jjr2001]

Thanks Wizard69, hopefully that would be limited to carbide bit tips!
With the VFD on the motor the max load current is settable and I have tested it.
So far so good, it trips out at my setting which is about 4 amps or about 900 watts.
The motor runs very cool. I have not seen it over 27 degrees C so far.

Cheers, JR