Grizzly G0602 Belt Drive Speed Reducer

[Fabrickator]

Since I’ve owned my Grizzly G0602 lathe, I’ve occasionally wished that I could slow the spindle speed down for certain operations. The lowest standard speed is 150 RPM and a little too fast for threading, turning and parting large diameters. Grizzly finally saw the need and the newer model (G0752) is equipped with a variable speed motor for an extra $450, and that’s a great thing. But for those of us that have the older models, we are stuck with only a couple of choices to slow these lathes down. The BEST way to do this and what some others have done is to set-up a variable speed drive system. Some have used DC tread mill motors and others have used AC frequency converters. Both require an electronic speed controller, a new motor and cost well over $300. I may still do this mod one day or upgrade my lathe, but for now I decided to take the “old school” approach because I did a lot of this when I worked in a prototype machine shop building industrial machinery.

I was looking inside the cover of my lathe one day while making a speed change using my “Quick Belt Change” mod that I introduced to G0602 owners a few years ago (http://www.projectsinmetal.com/forum/general-discussion/diary-of-a-new-g0602). I found that there is still a bit of space where I could build and mount a custom, triple reduction jackshaft. I began measuring and calculating and found that with different combinations of pulleys another dozen speeds are entirely possible, but that’s not necessary.

I verified my spindle speed calculations with my digital tachometer and also found that the standard speeds from Grizzly are not accurate, I got 180, 320, 507, 795, 1284 and 2466. I then optimized the various pulley combinations using commonly available parts to fill the gap below Grizzly’s 150 RPM and I settled on the 3 most practical low-end speeds of 75, 105, 147 rpm.

To use the 3rd reduction, you have to install the proper belt/pulley combination when you need it. It’s not difficult and takes only a couple of minute when used in combination with the “quick belt change” mod. I plan to only use it on rare occasions and take it off when not in use. I also developed this pulley/shaft spacer/belt/speed combination “cheat sheet” for quick reference to keep on the inside of the belt cover so I don’t have to remember what-goes-where when I need it.

I also modified a 5.5” pulley and was able to get 3 more lower speeds of 37, 60 and 80 rpm.

My total cost for the parts and materials was about $100. I used some scrap ¾” 6061 bar stock for the cradle. I bought a couple of surplus bearings, made the ½” shaft from a remnant and I purchased the retaining rings, pulleys and belts from McMaster-Carr. I figured out the correct dimensions to provide the desired ratios, the right position to mount it and a means to bolt it down without drilling or tapping one hole in the lathe. Instead, I utilized the void in the casting and made a nut plate for mounting it. I then used some epoxy putty to permanently mount the nut plate inside the casting.

I did most of the machine work on the mill and rotary table (RT) because I wanted to test my new RT tooling plate and work stops I recently made. The bearing bores could be done just as well, and probably quicker and easier in a 4-jaw chuck on the lathe.

I understand that most owners won’t feel the need to bother with this mod, but I’m sure that it will come in handy in the future and I’ll be happy to have the options available when the time comes.

Rick

Grizzly G0602 Lathe

LMS High-Torque Mini Mill

(my mill mods) http://www.hobby-machinist.com/threads/my-lms-mini-mill.22202/

 

[Franko]

Great project and good job, Fabrickator!

 

[RJSakowski]

It looks like a great mod for the 0602! I will be looking at doing the same. Thanks for sharing!

 

[ch2co]

If I hadn't bought my 0602 used from someone who had already added a 3-phase motor with a variable frequency inverter /
phase converter box, I doubt that I would have sprung for investing that much $$ into the machine. I probably would have
done something similar to what you are doing. I do love the inverter drive though, with low voltage controls that allow
for forward and reverse, and from 6 to 60 hz. variable speed which gets me down to around 40 RPM. I do think that
your system will provide more low end torque at the very low RPM's though. As usual for what I've seen of your
posts, well done.

Chuck the grumpy old guy

 

[RJSakowski]

Hi Rick ,

What diameter pulleys did you use? It looks like about 1" for the small pulley to get 37 rpm. Also, how do you tension the BD belt? I see a slot. Do you move the cradle to the right and tighten? How do you access the monting bolts? It looks tight.

Thanks,

Bob

 

[Kernbigo]

You don't need all that stuff, find a thread mill on the street corner and you are in business. The speed controller in the thread mill work fine after you change the pot and wire in a start and stop switch in the center wire of the pot(wiper). I have done 2 lathes and 2 band saws that way no problem.

 

[tmarks11]

... find a thread mill on the street corner and you are in business

I am guessing you mean treadmill... spell check strikes again!

A DC motor (like on a treadmill) provides better torque at lower speeds, however is a bigger challenge to mount as it won't have a foot to fit your machine. It is easier to find a 3 phase motor that fits the lathe without modifications.

Here is an example of the treadmill retrofit of the G0602 from Projects in Metal:
http://www.projectsinmetal.com/forum/general-discussion/g0602-variable-speed-motor/



Edit: to the OP, nice job on adding lower speed capability to your lathe...without sacrificing torque (which can be a problem when just slapping in a VFD and motor).

 

[Fabrickator]

What diameter pulleys did you use? It looks like about 1" for the small pulley to get 37 rpm. Also, how do you tension the BD belt? I see a slot. Do you move the cradle to the right and tighten? How do you access the monting bolts? It looks tight.

All of the sizes/speeds are in the pic of the chart. 1 1/2" , 2" and 2 1/2" pulleys. The large sizes are 4 1/2", and 5 1/2 x 1 1/2"for the lowest speed range (37 rpm).

As I said, a VFD or DC motor seem to be the best mod. But in my case right now where it sits, I can't get to the back of the lathe to set it up. Also, as was stated here, sometimes they lack the torque on the low-speed where a mechanical drive system provides full torque.

The mounting screws are on a bit on an angle right now, but I have a set of sweet ball-end, T-handle allens that work just fine. I was going to drill a couple of access holes in the brkt for the mounting screws, but it's not necessary with the allen wrench ($5).

Tension is done by tightening the BD drive belt (3rd reduction/sloted bkt) and then using the idler to tighten the DC belt.

 

[RJSakowski]

Thanks for the additional info, Rick

I didn't see 37 rpm on the chart and wondered if you had changed the smaller pulley as well.

I would agree that the vfd's lack low speed torque. My Tormach has a 3 phase vfd spindle drive and stalls very easily at the lowest speed setting. A pulley reduction actually increases the amount of spindle torque by the ratio of the pulley diameters.

I would be looking at lower spindle speeds for winding springs. Currently, I turn the spindle by hand.

Bob

 

[Greg Hudgins]

Man, that is one clean job there! I like the fact that you did not have to drill into the main body to attach the gear plate you built.
Do, you by chance, have a list of part numbers for the gears that you purchased for this modification? I would rather do this mod, and spend the saved money on tooling and such.
Again, great job.
Greg