Need help on decision. Was sent wrong mill and not sure what to do.

[Dabbler]

I notice that many cannot even think of a use for a sub 100 rpm speed.

When my mill is in back gear, with the VFD I can go down to 10 rpm. I use slow speeds below 100 RPM regularly. I run a 1/2" annular cutter, around 200-220 RPM and the bigger ones slower. Limits the heating problems and they stay sharp a lot longer. I've drilled at least 200 holes in .160 to ,250 tubing, some through the welds and that cutter is still sharp. I use between 120 and 160 RPM for 3/4", with soluble oil hand sprayed into the cut. for 1" and larger, all below 100RPM...

 

[tq60]

We have cut 3.5 diameter through 1 inch plate.

Slow is too fast...

Sent from my SM-G781V using Tapatalk

 

[Larry$]

At the same time 60 is really low, and I can't think of the last time I used 60 RPM for anything.

I use 60rpm or close for tapping all the time. Using the slower speed allows the tap to coast to a stop rather than needing to do an instant reverse.

My Bridgeport is a 1.5hp variable speed head. With a speed range of 60rpm to 4200rpm. It’s never lacked fo hp in any material. However I rarely use mills over 1” in diameter.

I have a VS 9x49 Jet knee mill, 3 hp 3 phase, and use 60rpm for power tapping all the time. Works great! I run my B&S edge finder at 900rpm±. The only time I use a wiggler is when I have a 3/8 collet in and am to lazy to change to a 1/2" for the B&S. I'm too deaf to have any noise from the mill bother me.
As for keep or send the PM mill, I'd say send, since that's what you wanted. If you don't you will forever kick yourself. If you are going to be producing multiples then I can see having a CNC, for one offs it is likely quicker to just do it manually.
As for moving a knee mill, not that big of a deal. Get the center of gravity as low as you can, have some help on hand. At most the price of a case of beer, after, the move!

 

[PNW_Guy]

Much of my comments about slow spindle speed is that it's a 6 speed box with 60-1,500 RPM and the one he ordered is variable between 50 and 3,200.

I don't use 60RPM (I know, some of you power tap more often than I do, or use large diameter hole saws). But I go over 1,500 RPM far more often than I drop below 100. I honestly don't understand why PM sells a *benchtop* mill with a 60-1,500 range.

 

[Larry$]

I honestly don't understand why PM sells a *benchtop* mill with a 60-1,500 range.

I agree about the 1500rpm top end seeming limiting. Seems like a good way to break small drills. But I still like to power tap and 60 rpm allows me to have very good control of stopping at the right point.

 

[mike96]

I have an 833TV I picked up new/second hand, and honestly I can say I am a tad disappointed in the spindle speed on this mill. I Have it converted to CNC and after getting everything all set up and making a few chips for the first time I found that the spindle gets hot after running around 2800 - 3000 RPM for about 15 minuets ... Hotter than s should IMO, hot enough that you almost cant touch the nose of the spindle. I contacted PM about it to see what the specs were for the spindle nut hoping that all I needed to do was check to ensure there was the proper mount of grease and that the spindle was not overly tight. After conversing with the PM guy Mike IIRC (90% sure it wasn't Mat) I was told that the spindle nut wasn't much more than hand tight (sorry I dont remember the actual torque spec off the top of my head) but I shouldn't have to worry about it as the machines "weren't meant to be ran at those speeds for extended periods of time".... Why advertise a mill that as capable of a specified speed if it is not usable at that RPM. Needless to say I still plan on taking the spindle apart and will probably at the very least replace whatever china bearings are in it with some much better Timken or SKF bearings. .. Between that and the waranty issue I am a tad upset with my PM experience so far.

 

[verbotenwhisky]

I have an 833TV I picked up new/second hand, and honestly I can say I am a tad disappointed in the spindle speed on this mill. I Have it converted to CNC and after getting everything all set up and making a few chips for the first time I found that the spindle gets hot after running around 2800 - 3000 RPM for about 15 minuets ... Hotter than s should IMO, hot enough that you almost cant touch the nose of the spindle. I contacted PM about it to see what the specs were for the spindle nut hoping that all I needed to do was check to ensure there was the proper mount of grease and that the spindle was not overly tight. After conversing with the PM guy Mike IIRC (90% sure it wasn't Mat) I was told that the spindle nut wasn't much more than hand tight (sorry I dont remember the actual torque spec off the top of my head) but I shouldn't have to worry about it as the machines "weren't meant to be ran at those speeds for extended periods of time".... Why advertise a mill that as capable of a specified speed if it is not usable at that RPM. Needless to say I still plan on taking the spindle apart and will probably at the very least replace whatever china bearings are in it with some much better Timken or SKF bearings. .. Between that and the waranty issue I am a tad upset with my PM experience so far.

That sounds like a bad bearing to me. I bought a set of Timken bearings from these guys https://www.qualitybearingsonline.com/ they are out of Britain and the bearings were cheeper than I could find them in the states by half, even with the customs/taxes they were cheaper and they arrived in a few days.

 

[skcncx]

@mike96 I'll be curios to know if you replace your bearings and the spindle doesn't get as hot anymore. I have run mine, an 833TV, brand new early this year, on and off the last few months, no long runs like you with 15 minutes or more of spindle spinning, but even shorter runs I noticed my spindle got very hot. I just don't know what to expect, it's my first mill ever.

 

[verbotenwhisky]

@mike96 I'll be curios to know if you replace your bearings and the spindle doesn't get as hot anymore. I have run mine, an 833TV, brand new early this year, on and off the last few months, no long runs like you with 15 minutes or more of spindle spinning, but even shorter runs I noticed my spindle got very hot. I just don't know what to expect, it's my first mill ever.

The mill I have doesn't even get warm. I jammed up a bit in a deep hole and screwed up a bearing, my fault and had to replace one.

 

[Larry$]

I was just milling a hex opening and used an 1/8" four flute endmill @ the top speed of my Jet, (3400±) Light cuts in mild steel worked very nicely. 5C collet block, the knurled holder has set screw & a hole for a tommy bar or can be setup in the tailstock die holder on the lathe. Speed is nice to have for small tooling. Slow is great for big annular cutters, big drills, large fly cutters & power tapping.