# Larger drive pulley for Grizzly 4003 to slow machine down?



## ridgeway (Aug 26, 2013)

Anyone know if its possible to put a larger drive pulley on a Grizzly 4003 lathe to slow the machine down?  The slowest it goes is 70 RPM and I have to be extremely quick threading up to a shoulder.  I would like the ability to run maybe down to 50 RPM.   

Not sure if his would be possible or not.  Any other ideas?


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## Tony Wells (Aug 26, 2013)

Drive pulley has to be smaller, or drive pulley larger to effect a speed change in that direction, and of course, all the charts will need to be changed to suit if you plan on a permanent change. If you drive with a larger pulley, speeds will be higher, not lower. Drive pulley being on the motor, that is.


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## SEK_22Hornet (Aug 26, 2013)

I took a look at the parts list and I suspect that changing the pulley on the headstock would be quite a project - you might take a look at the motor pulley and see if you could go any smaller with it. Otherwise you might see if there is any way you could add a jack shaft between the motor and the headstock.  Things look pretty tight in there, so I would say your best shot would be if you can use a smaller motor pulley.


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## Ray C (Aug 26, 2013)

Also, if you're changing the pulley/sheave diameters, don't go with too small of a radius as it will heat up and wear-out belts.  Your system probably has a 1/2" or 5/8" v-belt and if it does, you can look up the minimum recommended bend radius or diameter for that type of belt.  If you have X designated v-belts (which have split notches in the V) you can go with slightly smaller diameters compared to a solid belt.  It makes a big difference in the amount of slip and heat generated if you don't do it right and you'll be changing belts regularly...


Ray


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## fastback (Aug 27, 2013)

Here is another way to slow down the machine.  You could replaced the motor with a 3 phase and use a VFD.  This would not affect the speed chart when run at of 60 Hz. I know that this would be relatively expensive, but on the plus side you would have it all.  You could change the speed with a twist of the potentiometer.  I have this set up on my 10L and can reduce the spindle speed all the way down to 25 RPM if needed.


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## ridgeway (Aug 27, 2013)

Yeah, my bad on pulley size...I should have remembered that from my dirt bike days changing sprockets.

I really do like the VFD idea...Just have to hunt around for a 3 phase motor that would fit.  My lathe is in the open, so no problem accessing it.  VFD's are relatively cheap...i'm sure the motor is where the cost is!

Now, when looking for a motor.  My lathe has a 2 HP single phase, what would the equivalent be in 3 phase?  Won't the limitation of the VFD create a certain reduction in power?


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## Ray C (Aug 27, 2013)

See Post #1 of this thread for a motor with probably will be a drop-in replacement.  I don't gaurantees that though.  Also, somewhere in that thread I discuss my views of gear changing when VFDs are employed.  http://www.hobby-machinist.com/showthread.php/11649-PM-1236-VFD-Conversion?highlight=1236+conversion


Ray





ridgeway said:


> Yeah, my bad on pulley size...I should have remembered that from my dirt bike days changing sprockets.
> 
> I really do like the VFD idea...Just have to hunt around for a 3 phase motor that would fit. My lathe is in the open, so no problem accessing it. VFD's are relatively cheap...i'm sure the motor is where the cost is!
> 
> Now, when looking for a motor. My lathe has a 2 HP single phase, what would the equivalent be in 3 phase? Won't the limitation of the VFD create a certain reduction in power?


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## fastback (Aug 27, 2013)

Ray, I read the thread regarding your 3 phase upgrade.  I am not sure I agree with your analogy of the crank shaft and transmission.  I don't believe that you would be placing that much additional work load on the drive train since all you will be doing is changing the motor speed by just a small amount compared to a gasoline engine.

I use all three speeds on my lathe I just have more flexibility in each given range.  Also there is a max speed you can get out of a VFD due to heat from the motor etc..  We are not pulling hole shots in 3rd gear.  Keep in mind that the HP range we are working with is 1 or 2 HP not 2, 3 or 4 hundred.  Gasoline engines have a sweet spot where the max HP and torque are found.  This is usually at the upper end of the RPM band. At lower speed they tend to lug.  I think we are talking apples and oranges here.

Just another opinion.


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## Ray C (Aug 27, 2013)

Fine and well but, do realize that the stress on a gear is inversely proportional to the square of rotation and that torque transmission through gears is related to the ratio of the gear sizes -and related to that, is that smaller gears (with fewer teeth) put all that torque through one individual tooth at a rate much faster than a large gear.  Those are the two factors involved -regardless of analogies to automobiles.

Ray




fastback said:


> Ray, I read the thread regarding your 3 phase upgrade. I am not sure I agree with your analogy of the crank shaft and transmission. I don't believe that you would be placing that much additional work load on the drive train since all you will be doing is changing the motor speed by just a small amount compared to a gasoline engine.
> 
> I use all three speeds on my lathe I just have more flexibility in each given range. Also there is a max speed you can get out of a VFD due to heat from the motor etc.. We are not pulling hole shots in 3rd gear. Keep in mind that the HP range we are working with is 1 or 2 HP not 2, 3 or 4 hundred. Gasoline engines have a sweet spot where the max HP and torque are found. This is usually at the upper end of the RPM band. At lower speed they tend to lug. I think we are talking apples and oranges here.
> 
> Just another opinion.


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## ridgeway (Aug 27, 2013)

Thanks Ray!


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## fastback (Aug 27, 2013)

Ray, I know what you are saying, but we are not talking huge speed changes.  Most of the changes are to slower speeds by maybe 10 or 20 rpm.  Look at the new 8 and 10 inch SB lathes they don't have any back gears its all variable speed drive. 

I am not trying to argue the point I just don't think the gear train on a lathe is all that weak.  There are a ton of people out there with these VFD's having a lot of success and no problems.  My set up is over 3 years old and I have had no problems what so ever.  


One other thing to mention is with the VFD, as you know, you can set the min and max settings.  This way you can get right where you want in the RPM range.  I doubt that any of us want to damage our equipment.


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## Ray C (Aug 27, 2013)

Maybe there's a misunderstanding...  I contend that it's best to use the normal gearing on the lathe as much as possible and vary the speed on the VFD only so much as to allow it to span the gaps from one gear speed down to the next lower one.  In my case, I have the VFD programmed to allow 45 to 60 Hz.  (maybe it's 50 to 60, can't remember anymore).  If I can't find a good RPM in that range, I change gears and tweak speed to get what I want.

I'm not an advocate of leaving the gear in basically one fixed mid-position and using the VFDs wide range of frequency to find the speed you want.  This would entail allowing frequency to range from probably 20 to 80Hz -possibly even a wider range.  This I feel is bad medicine.  There were a few folks here saying they pretty much did this.  I think you can get away with it if you have an older leather belt drive system but, for the sake of the motor, I don't think running it below about 20% of rated speed is good for it nor do I feel running it above rated speed is good.  Of course, if the motor says it's ok then, so be it.  Still though, running small gears at significantly higher speeds than they were meant to go, is not a good thing.

I do know from my continuing education from Matt, that not all lathe gears are born equal.  On really high end, high speed lathes, they are hardened, individually balanced and are far more sophisticated than the typical flat-root, 20[SUP]o[/SUP] involute crown gears that we are accustomed to seeing. EX:  I can't remember the name of the mill but, there's a CNC mill out there that is based off the RF45 design.  It has top speeds of 5000 RPM.  The gears in that thing probably cost 4-5 times as much as the gears Matt has installed in his machines...

BTW, I've got VFD on my lathe for about a year (maybe less) and it's the greatest thing since sliced bread!  -Would be better if I took the time to finally figure-out and program the jog function .

Ray




fastback said:


> Ray, I know what you are saying, but we are not talking huge speed changes.  Most of the changes are to slower speeds by maybe 10 or 20 rpm.  Look at the new 8 and 10 inch SB lathes they don't have any back gears its all variable speed drive.
> 
> I am not trying to argue the point I just don't think the gear train on a lathe is all that weak.  There are a ton of people out there with these VFD's having a lot of success and no problems.  My set up is over 3 years old and I have had no problems what so ever.
> 
> ...


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## fastback (Aug 28, 2013)

I guess we are back on the same page.  My VFD is set for 35 to 90Hz.  I tend to use it more on the lower end for threading.  What is nice about the VFD is you can tweak the speed for the cut being made.  These things are great sliced bread is an understatement.


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## Ray C (Aug 28, 2013)

Yes, for threading it helps. I tend to tread as fast as possible.  The gearbox low speed is too slow and the next speed up is a bit too fast so I knockit down just a touch with VFD.

My favorite use is when facing an ornamental piece.  If I start the cut from the outside and work toward center, I gradually increase the speed as it progress thus roughly keeping the same SFM and the part gets a nice even appearance.


Ray



fastback said:


> I guess we are back on the same page. My VFD is set for 35 to 90Hz. I tend to use it more on the lower end for threading. What is nice about the VFD is you can tweak the speed for the cut being made. These things are great sliced bread is an understatement.


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## iron man (Aug 28, 2013)

I installed a DC 2 1/2 horse commercial tread mill motor on my lathe with a dc PWM speed control I can get it down to a crawl very nice for threading cheap and easy to find. Ray


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