# Maximum Safe Rpm For A Grizzly G4003g



## Xiansheng (Apr 8, 2015)

Hi Everyone,

I am planning to install a VFD speed controller on my lathe, which is the equivalent of a Grizzly G4003G.  I plan to use a speed range of about 25 to 2,500 RPM, but I will be grateful for any advice about the higher limit.  Is the lathe capable of being run at 2,500 RPM?


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## fixit (Apr 8, 2015)

2500 I would say OK, but 25000 NO WAY

fixit


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## planeflyer21 (Apr 8, 2015)

/\/\/\/\ I concur with fixit.

2500 is plenty for what you would want to do.  25 rpm is an awesome slow speed!


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## 007 (Apr 8, 2015)

In my opinion, just because your car and go 100 mph is it safe to do all the time? I recommend 70% of top end for all the time, otherwise your car will wear out prematurely. Your lathe will thank me also, if you use the same advise.


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## Xiansheng (Apr 8, 2015)

Hi Everyone,

First, I apologise for my typo where I suggest that I want to run the lathe at 25000 RPM.  I realise that even it it were possible and needed, it would be insane and a rather nasty smash would be inevitable.  I also don't plan to regularly run the lathe at 2500 RPM, but would like the capability for very small parts.  As for the 25 RPM, I want to be able to do screw-cutting at what I consider a safe speed, especially if forced to keep the half nuts locked and stop the lathe when cutting metric threads.  Years ago I used to use lathes with back gears that permitted that sort of low speed which was very comfortable, whereas this lathe's minimum RPM is 70, which is too fast for some screw-cutting or other operations.  To illustrate what I mean, when winding a inductor coils or making springs, a slow speed is very preferable.  Regards  Xiansheng


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## wrmiller (Apr 8, 2015)

Not sure as to the actual experience of anyone running a 4003G at 2500 rpm, but it capability of doing so will depend upon factors like how well the spindle is balanced (or not) what type of bearings are used in the headstock, and what the remainder of the gear train can support.

I would look at the gears (quality, mesh, etc.) and other components more closely if you intend to do a large number of small parts at 2k+ rpm. If you are thinking of doing this only occasionally, then the geartrain is less critical. You still may need to upgrade the spindle bearings though.

Just thinking out loud...


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## coolidge (Apr 8, 2015)

The max speed on a G4003G is only 1,400 rpm I don't think it would be wise to assume it can take 2,500 rpm you might take a piece of casting or gear to the face.


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## mksj (Apr 8, 2015)

When threading, just turn the speed pot down  as you get to the end. Otherwise add an electrical stop switch and use the vfd electrical brake. I use a proximty sensor, postion stop is better than 0.001. Probably max speed of 2000, other than mechanical issues, lubercation may also be an issue. You will also get a better finish going to 3 phase.


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## tmarks11 (Apr 8, 2015)

I don't think you will take a casting in the face, but you will accelerate bearing wear.  That being said, I doubt that the spindle bearings will be overstressed at 2500 rpm... the spindle bearings are quality NSK, and are rated for a significantly higher rpm.  

Now will your chuck hand that speed is a different question.  Four jaw chucks are generally only rated for slower speeds than three jaws.  Cast iron chucks for lower speed than steel.  If you don't know the speed rating of the chuck, than don't chance it.  

You would definitely have no problems with a 5C chuck at those speeds.


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## dave2176 (Apr 8, 2015)

Mine has P5 NSK bearings. I don't think the spindle and bearings is the issue. I think it will come down to gear quality and alignment in the headstock. Wish they had helical cut gears.
Dave


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## Ianagos (Apr 9, 2015)

Yea as long as oil is getting to those bearings you should be fine. Bearing in lathe spindles are way better than they need to be in my opinion. They named to add some qaulity to other stuff before going into super precision bearings.


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## Xiansheng (Apr 9, 2015)

Hi Everyone,, To respond to the several responses that have been made in the last 10 hours, I realise there might be issues with the headstock gears and bearings, and I believe more risk with the gears.  I simply will replace the bearings with the best I can buy if they fail, and likewise with the gears, that said, I repeat my previous comment that I don't intend to use 2500 RPM except on rare occasions, for small jobs.  I also would not use a chuck or faceplate at such speeds, because there is too high a risk that they will disintegrate.  Collets would be my only choice at 2500 RPM.  I remember as an apprentice using a high-speed Chaublin lathe for small work and it was only used with collets (a very nice lathe, I must say!).  Another reason for the 2500 upper limit is my opinion that the present maximum RPM of 1440 RPM is limiting.  Many jobs will not  be machined at their correct cutting speed at this limit.  Coolidge's suggestion to use a proximity sensor and vfd electrical brake is interesting and thought provoking.


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## coolidge (Apr 9, 2015)

I think that was mksj's suggestion.


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## mksj (Apr 10, 2015)

FYI: VFD proximity sensor stop
http://www.hobby-machinist.com/threads/vfd-proximity-sensor-stop.32816/

Regarding safe operating speed, although the bearings may be rated for higher speed, lubrication to the bearings is probably the rate limiting issue when using splash lubrication. Most lathes in this size/type limit out at around 2000 RPM. It may do higher, for short periods, but if the bearings go it could cause additional damage. I would use an ISO32 oil (which is the standard for most Grizzly lathe gear heads), as higher viscosity oils cause too much frictional drag.

http://www.practicalmachinist.com/v...eadily-available-oils-will-work-pinch-278701/
"Most of those small lathes will do 2,000 RPM. It's not the gears, its the bearings. An oil that's too viscous will heat those bearing up in a hurry if you run a very fast RPM. Almost all the lathes that I've seen in 15" and under take ISO-32 in the headstock. IMO, Vactra would probably wipe out a set of bearings if you ran very fast. It just doesn't squeeze out of the way like hydraulic oil does. Somewhere, if I haven't thrown it out, I've got a calculation sheet from one of my lube schools. You put in all of the bearing data plus the RPM and do about 20 calculations an end up with a maximum film thickness of the oil/grease you can use."


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## stupoty (Apr 10, 2015)

If  your vfd can have more than one ramp up duration that might be nice to the gears to give it a less harsh acceleration period or manualy ramp it up using the speed pot.

Sensible about the no chuck at high rpm , i cant even imagine a Big  3 or 4 jaw at that speed. Wow

The other thought, as was said about oil and stuff is how does it move the oil in the head stock?  If theirs any kind of impela it will be under more load at the higher rpm, if its just the gears flinging the oil thats probably a non issue.

With the low rpm side i have managed to heat up my bench mill motor quite significantly hot doing some extended work at a much lower rpm due to the cooling fan not running fast enough (its 0.75kw and gets warm to the touch in normal 50-65 hz range)  threading would probably be running the motor for reasonably long times, although i suppose it would generally  be short threads you would want to do at that speed.

Stuart


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## berniehernandez (Mar 16, 2016)

If you run the lathe at low RPM's, the oil will not reach the spindle bearings. Rev the speed up to sling the oil to upper part of the gearbox. It then flow into the holes for the spindle bearings.


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## coolidge (Mar 17, 2016)

I would just point out that the G4003G has several more bearings in the headstock that are not NSK and cost like $12


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