Grizzly 4003G Speed Question

digadv

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I'm down to my final decision between the PM1236 and the Griz 4003G. The top-end RPM of the PM1236 is 1800 and the 4003G is 1400. My question is will I need the extra 400 RPM at the high end? In my research I understand that fpm is the thing to look at and I've run some online calculators - many confusing to me with all of the "knobs" to turn. My anticipated uses for the lathe range from using aluminum to stainless steel. I recall in one instance running the calculator that turning 1/2 alum alloy with a HSS insert would require over 3800 RPM - could this be correct or did I possibly mis-configure something?

As a follow up question ... have folks safely achieved higher speeds on this lathe with a VFD conversion?

Many thanks and Merry Christmas to all!
 
More top speed is always a good thing, but at what cost? If you could list all the speeds for both machines, and give us an idea of what you plan to do with the lathe, we could no doubt be much more helpful.

Speeds shown on manufacturer's recommended speed charts are for production work in an environment where everything is optimized -- very rigid machines, fire hose flood coolant, etc. Tools and machines will not last as long in that environment without paying careful attention to a lot of details. In a hobby shop, dial it down some, especially at first, and see how it works for you. High surface speeds often do help the achieved finish. Good work can be done with machines that are much more humble.

Three phase machines can be sped up with a VFD, but only to a certain point without destroying spindle bearings and motor, and perhaps becoming unsafe to the operator with some components. A 25% increase (and decrease) is often quite possible and usable, but "it all depends."
 
Thanks for the reply. Here are the speeds of the two machines (from spec sheets):

4003G: 70, 200, 220, 270, 360, 600, 800, 1000, 1400 RPM
PM1236: 65-1800 RPM in 18 steps

Uses for the lathe range from small parts out of aluminum/steel to threading various fittings to eventually rechambering SS barrels.
 
Thanks for the reply. Here are the speeds of the two machines (from spec sheets):

4003G: 70, 200, 220, 270, 360, 600, 800, 1000, 1400 RPM
PM1236: 65-1800 RPM in 18 steps

Uses for the lathe range from small parts out of aluminum/steel to threading various fittings to eventually rechambering SS barrels.

Small = Speed most of the time

Full disclosure - I am a PM fan. I like the equipment they sell and from my experience, their customer service is in a league far above that of the Griz.
 
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So the PM has a lower low speed, a higher high speed, and 18 speeds compared to 9 speeds. If that is the only criterion for choosing between them, then you have your answer...

Barrels are still small diameter, and will use speeds well above the lowest -- except perhaps for power chambering with a reamer, which is a slow speed operation.
 
I got a PM1236 this year and the 1825 rpm is just adequate for CCMT tooling. If your turning round bar under 1" with carbide insert tools you need speed for sure. Grizzly models didn't compare well feature wise for the money and PM has the better warranty.

I would suggest getting a heavier model with a foot brake. I had to wait for mine, but I like my choice so far. I figured eventually I'll need that foot brake. :)
 
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I have the Grizzly G4003G. Love the machine and never use over 1000rpm even when doing small parts despite what the books says. They come out fine. Things happen a bit to fast for my comfort level when spinning @ 1400.
 
Speeds are a greater concern when using carbide tooling, especially inserted carbide. Most hobby class lathes cannot get anywhere near the optimal speeds unless you're turning harder materials with largish diameters - they're too slow. However, carbide will cut at lower speeds, as most hobby guys will attest so I wouldn't worry over much; the lathe will work.

On the other hand, HSS is always an option and most lathes can use HSS quite effectively. For example, you can easily turn 1/2" OD aluminum at 1500 rpm and produce a mirror finish. The only issue with HSS is that you have to grind your own or use an inserted HSS bar like those from AR Warner. My 11" lathe has a top speed of 2200 rpm and it works fine with HSS tooling for almost anything I do. YMMV.
 
The carbide tooling will work better at lower speeds if you get positive rake tooling, not neutral or negative, for smaller lathes and work. Chip breakers and sharp cutting edges can make neutral rake tooling cut like they are positive tools.
 
This seems to be a thread where the following question is pertinent::

The G4003G has 2HP
There are a variety of videos on the net concerning negative rake insert tooling.
Many of these videos suggest CNMG tooling needs more HP than CCMT, etc.

Does the 2HP the G4003G has fall into the "not enough" or the "about enough" category wrt negative rake insert tooling?
 
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