833T & 1340GT Questions

I agree with a lot of what’s been said here:

Replace the belt on the 1340 with a Gates Tri-power.

I would stick with Dorian (my choice) or Aloris for the quick change tool post rather than trying to save a few dollars on an off-brand alternative.

Avoid the Dorian “First time buyers kit” that includes the tool post and some tools and tool holders - it looks like a good deal but some of the tools they include are highly specialized and not useful for most people getting started.

That said, I would NOT buy Aloris or Dorian QC tool holders for square shank tools or boring bars. The Dorian BXA size tool holders will take >3/4" shank tools, but do so by lowering the bottom ledge that registers the tool in the holder. To run 5/8" or 1/2" shank tools in the Dorian holders, you have to put a spacer under the tool. The Aloris BXA tool holders will take 1/2" and 5/8" shanks but will not accommodate 3/4“ shanks. In contrast, the BXA holders Matt sells at Precision Matthews, as well as the BXA size tool holders from All Industrial Tool supply ($15 each) or CDCO ($12) will also take a 3/4" shank tool, but accommodates them with different geometry that doesn't require a spacer under 1/2" and 5/8" shank tools.

Before I down-graded to a PM935, I had the Rong Fu 45 square column mill/drill that was similar to the PM833. I got very tired of cranking the head up/down manually, so I recommend you get the Z-axis power feeder option if you can swing it.

Several PM users have complained about blowing capacitors (mill & lathe), or harmonic vibration induced into machined parts from the factory supplied single-phase motors (lathe). If you can see your way to a 3-phase setup, you will have fewer issues. Either run each machine on a VFD which gives variable speed control (mksj is the guy here to help with that) or get a simple phase converter for your two machines.

Lathe chucks depend a lot on what kind of work you’ll do. Matt sells some nice 3- and 4- jaw upgraded chucks. I use an ER40 collet chuck the most often and made my own, but I hear good things about the Shars Set-tru (I no longer allow any Shars in my shop).
 
davidpbest said:
Before I down-graded to a PM935, I had the Rong Fu 45 square column mill/drill that was similar to the PM833. I got very tired of cranking the head up/down manually, so I recommend you get the Z-axis power feeder option if you can swing it.
Click to expand...

David, it's interesting to hear that going to the PM935 knee mill from your RF 45 was a downgrade for you. Could you elaborate on why that was, I have been led to believe that knee mills were more rigid and capable than square column ones.

Thanks,

John
 
matthewsx said:
David, it's interesting to hear that going to the PM935 knee mill from your RF 45 was a downgrade for you. Could you elaborate on why that was, I have been led to believe that knee mills were more rigid and capable than square column ones.

Thanks,

John
Click to expand...
With some reluctance, I will share my views on your question. My reluctance stems from the fact that conventional wisdom dictates that knee mills are better than benchtop mill/drills, and I have no desire to start a war of an alternative point of view. But, having owned both, and put them through their paces, I see it somewhat differently.

First off, the word “downgrade” was probably a bad choice. In some respects, moving from an original RF-45 (the real one made in Taiwan) to the PM935 has been a disappointment, in other respects I enjoy many of the new features that come with a knee mill. I essentially traded one set of constraints and restrictions for another set of constraints and restrictions.

My primary motivation in making the change was to get onto a milling platform that had power feed on X, Y and the head or knee. Adding power feed to the Y-axis and the head on an RF-45 is not easy. Like you, I bought into the notion that a knee mill would be better overall.

Several people warned me that I would find the J-head design a disappointment, but I didn’t listen or research that aspect and plunged forward with the purchase of the PM935. As it turns out, the original head on my 935 was defective, and it took a good six months of effort to diagnose, change out various parts, ultimately coming to the conclusion that the head was grossly defective in some manner dealing with the spline drive system, spindle alignment, etc. Matt at Precision Matthews came through in the end, and ultimately supplied a complete new head unit, which resolved the problems. That said, in the process of all this I ended up becoming fully educated on the J-head design, and I am not impressed - particularly the way the back gear system works and how the power downfeed works on the quill. In comparison to how an RF-45 geared head achieves 60 to 3000 RPM, and how the power downfeed is designed, the J-head is positively 18th century. If you’re interested in the complete saga of my J-head issues, it is completely documented here.

Like I said, I have a new head unit now, and although I’m not fond of the J-head design in general, it works and I have learned to live with its idiosyncrasies.

I was attracted to the PM935 because it had a small footprint, and would fit in the same general space allotted for my RF-45. It was also short enough to fit in my low ceiling height of 82-inches. I considered other knee mills, but every one of them required 84” or more, which I did not have. I was aware that I would be buying a junior-sized knee mill - one that weighed 1,000 pounds less than conventional knee mills. Still, it was considerably heavier than my RF-45.

I had hoped the 935 would be a more rigid machine but that has not proven to be the case. The expressed “common wisdom” is that knee mills are more rigid than bench top mill/drill machines, and I’m certain that is true when a smaller mill/drill weighing 400 pounds is compared to a 2,500-pound knee mill.

However, the RF-45 square column mill has a very beefy column, attached to a beefy base with no knee to flex or gib interposed, and a head unit attaches directly to the column instead of being placed out at the end of a cantilevered ram. The ram on the 935 provides additional Y-axis room for sure, but it also puts a 350-pound head unit at the end of what is essentially a potential springboard. Add to that ram a knuckle that facilitates head nod as well as tilt, and you have another component that can contribute to rigidity weakness. In my opinion, the knuckle on the PM935 is undersized and the bolting arrangement that locks it in pitch and yaw is insufficient to keep the head tram in alignment under heavy loads made possible by the 3HP motor. This is just my opinion, and certainly not empirically proven, but in contrast to the knuckle design on an Acra or Wells-Index, the knuckle on the PM935 is a weak point. To be sure, I never experienced the head being driven out of tram on the RF-45 under the heaviest of loads, but I have experienced that on the PM935.

So, put a very heavy head at the end of a cantilevered ram, and interpose a marginally sized knuckle in the middle, and I think you can see why a junior sized knee mill might be less rigid than a beefy direct-to-column head attachment machine like the RF-45.

I am also fully aware that a 2,500-pound Wells-Index, Acra, or Sharp knee mill will have better rigidity than the RF-45 benchtop mill/drill. But the 1500-pound PM935 is in a different league; supporting the same 350-pound J-head on a cantilevered ram arrangement.

How does this translate in practice? Have a look at this video.

The same test on my RF-45 shows a head deflection of 0.0003” - that’s 8 times less deflection than the PM935. Matt at PM confirmed that 30 pounds of pressure on the PM935 should show about 0.002” deflection as my test shows. “This is normal” was his specific comment.

I realize this specific test is probably insufficient, or even flawed in its attempt to ascertain the rigidity of the machine or make empirical comparisons to other machines regarding rigidity. But I can say, after plenty of experience and lots of time milling 6061, 303/304 stainless, 4041 and 1018 steel, I was able to drive my RF-45 harder than the PM935, and get better surface finish and tolerances for any given feeds/speeds equivalency. My general impression in comparing the RF-45 to the PM935 in terms of rigidity is this: in achieving any given surface finish or machined feature tolerance, I could achieve about 30 percent higher material removal rates on the RF-45 in comparison to the PM935. And then there is the issue of head tram being forced out of alignment under heavy loads as mentioned above – something other PM935 users have confided to me privately.

The last four videos in the following series might also be interesting viewing on this topic: click here.

I had decided previously not to post on this publicly, because it will likely bring out the wrath of others (“you are full of crap, my PM935 runs circles around my buddy’s Grizzly whatever” or “your tests are faulty, or you’re gibs are loose, or your dial indicator needs calibration” kind of flaming) and stir up endless debate (“In my 400 years as a machinist, I’ve never seen a bench top mill that could be even close in performance to the cheapest knee mill” kind of thinking), and also because I don’t want to come across as trashing PM, or the PM935. Precision Matthews has supported me well. The PM935 is a very nice junior sized mill and I have recommended it to others with full disclosure of its limitations in addition to its virtues.

Now I will sit back and hope the flaming isn’t too harsh. :)
 
Interesting.
Nobody warned me about the j-head.
I wish they had.
 
Last edited:
Thank you very much for responding, I understand why you haven't posted about this before but it seems very pertinent to us hobby machinists with limited space.

I previously had a Gorton 1-22 which I think fits into the larger knee mill category but I lost that one when I closed my old shop and couldn't move it into my garage. I'm now building my own small CNC mill/drill but eventually see myself looking for another manual machine.

You've definitely given me something to think about as I move forward and I hope your post doesn't generate too much controversy. At the end of the day I guess what you're saying is you can't deny physics and it's impacts in the shop.

John
 
davidpbest said:
With some reluctance, I will share my views on your question. My reluctance stems from the fact that conventional wisdom dictates that knee mills are better than benchtop mill/drills, and I have no desire to start a war of an alternative point of view. But, having owned both, and put them through their paces, I see it somewhat differently.

First off, the word “downgrade” was probably a bad choice. In some respects, moving from an original RF-45 (the real one made in Taiwan) to the PM935 has been a disappointment, in other respects I enjoy many of the new features that come with a knee mill. I essentially traded one set of constraints and restrictions for another set of constraints and restrictions.

My primary motivation in making the change was to get onto a milling platform that had power feed on X, Y and the head or knee. Adding power feed to the Y-axis and the head on an RF-45 is not easy. Like you, I bought into the notion that a knee mill would be better overall.

Several people warned me that I would find the J-head design a disappointment, but I didn’t listen or research that aspect and plunged forward with the purchase of the PM935. As it turns out, the original head on my 935 was defective, and it took a good six months of effort to diagnose, change out various parts, ultimately coming to the conclusion that the head was grossly defective in some manner dealing with the spline drive system, spindle alignment, etc. Matt at Precision Matthews came through in the end, and ultimately supplied a complete new head unit, which resolved the problems. That said, in the process of all this I ended up becoming fully educated on the J-head design, and I am not impressed - particularly the way the back gear system works and how the power downfeed works on the quill. In comparison to how an RF-45 geared head achieves 60 to 3000 RPM, and how the power downfeed is designed, the J-head is positively 18th century. If you’re interested in the complete saga of my J-head issues, it is completely documented here.

Like I said, I have a new head unit now, and although I’m not fond of the J-head design in general, it works and I have learned to live with its idiosyncrasies.

I was attracted to the PM935 because it had a small footprint, and would fit in the same general space allotted for my RF-45. It was also short enough to fit in my low ceiling height of 82-inches. I considered other knee mills, but every one of them required 84” or more, which I did not have. I was aware that I would be buying a junior-sized knee mill - one that weighed 1,000 pounds less than conventional knee mills. Still, it was considerably heavier than my RF-45.

I had hoped the 935 would be a more rigid machine but that has not proven to be the case. The expressed “common wisdom” is that knee mills are more rigid than bench top mill/drill machines, and I’m certain that is true when a smaller mill/drill weighing 400 pounds is compared to a 2,500-pound knee mill.

However, the RF-45 square column mill has a very beefy column, attached to a beefy base with no knee to flex or gib interposed, and a head unit attaches directly to the column instead of being placed out at the end of a cantilevered ram. The ram on the 935 provides additional Y-axis room for sure, but it also puts a 350-pound head unit at the end of what is essentially a potential springboard. Add to that ram a knuckle that facilitates head nod as well as tilt, and you have another component that can contribute to rigidity weakness. In my opinion, the knuckle on the PM935 is undersized and the bolting arrangement that locks it in pitch and yaw is insufficient to keep the head tram in alignment under heavy loads made possible by the 3HP motor. This is just my opinion, and certainly not empirically proven, but in contrast to the knuckle design on an Acra or Wells-Index, the knuckle on the PM935 is a weak point. To be sure, I never experienced the head being driven out of tram on the RF-45 under the heaviest of loads, but I have experienced that on the PM935.

So, put a very heavy head at the end of a cantilevered ram, and interpose a marginally sized knuckle in the middle, and I think you can see why a junior sized knee mill might be less rigid than a beefy direct-to-column head attachment machine like the RF-45.

I am also fully aware that a 2,500-pound Wells-Index, Acra, or Sharp knee mill will have better rigidity than the RF-45 benchtop mill/drill. But the 1500-pound PM935 is in a different league; supporting the same 350-pound J-head on a cantilevered ram arrangement.

How does this translate in practice? Have a look at this video.

The same test on my RF-45 shows a head deflection of 0.0003” - that’s 8 times less deflection than the PM935. Matt at PM confirmed that 30 pounds of pressure on the PM935 should show about 0.002” deflection as my test shows. “This is normal” was his specific comment.

I realize this specific test is probably insufficient, or even flawed in its attempt to ascertain the rigidity of the machine or make empirical comparisons to other machines regarding rigidity. But I can say, after plenty of experience and lots of time milling 6061, 303/304 stainless, 4041 and 1018 steel, I was able to drive my RF-45 harder than the PM935, and get better surface finish and tolerances for any given feeds/speeds equivalency. My general impression in comparing the RF-45 to the PM935 in terms of rigidity is this: in achieving any given surface finish or machined feature tolerance, I could achieve about 30 percent higher material removal rates on the RF-45 in comparison to the PM935. And then there is the issue of head tram being forced out of alignment under heavy loads as mentioned above – something other PM935 users have confided to me privately.

The last four videos in the following series might also be interesting viewing on this topic: click here.

I had decided previously not to post on this publicly, because it will likely bring out the wrath of others (“you are full of crap, my PM935 runs circles around my buddy’s Grizzly whatever” or “your tests are faulty, or you’re gibs are loose, or your dial indicator needs calibration” kind of flaming) and stir up endless debate (“In my 400 years as a machinist, I’ve never seen a bench top mill that could be even close in performance to the cheapest knee mill” kind of thinking), and also because I don’t want to come across as trashing PM, or the PM935. Precision Matthews has supported me well. The PM935 is a very nice junior sized mill and I have recommended it to others with full disclosure of its limitations in addition to its virtues.

Now I will sit back and hope the flaming isn’t too harsh. :)
Click to expand...
No flaming from me, that was very helpful in fact, so thanks for posting your thoughts/findings and experience. Definitely something for me to keep in mind when I'm ready to replace my current mill with something more substantial.
 
Can't really cheat the laws of physics, mass/size and leverage all play into the flex equation. Do not loose track that the RF 45 is much more compact and the Y travel is a 8.2" vs 12" for most knees. You also loose about 1" plus if you add a DRO, which was a limiting factor on my previous square column mill. The 833T has a Y travel of 11" and heavier than the RF45, so should be interesting comparison. Another big question on the current RF-45 mill is quality issues discussed in other threads. When I upgraded to a knee, I went with a 9x42 Acra/Sharp which is around 2400 lbs, and I still consider it a light weight mill compared to some of the others I have used. Still, if you have the room and can get it into your space, there is a benefit to a heavier machine. The 42" table is a bit small, but given that I am 5' 6" on a good day I didn't want anything bigger. I can barely get the vise and rotary table on the table at the same time. In hindsight I might have gone with a 49/50" table with the power feeds. I went with the X and Z power feeds which made life so much easier. I get almost mirror finish using face mills and almost no ridging with multiple passes.

As far as the J head, yes primitive beast, but works. They have been around for decades and are pretty much unchanged. Adding to that the electronics/VFD models are also as primitive when they could do so much more. The market is very small, and no one is going to invest in a major redesign at this level. CNC is a different ballpark, yes there will always be a place for manual machines, but these days it is getting much smaller. I can say that I have a J head on my knee mill which came with a factory VFD, and it works reliably and is rigid on my mill. The stock VFD control was pitiful, and of course it was the first thing I modified. So forward is always forward, reverse is always reverse, even in back gear. Added auto reverse for tapping with auto start/stop. I much prefer 3 wire control for mills with them located at the knee, big safety issue for me.

Jason, thank you for your kind comments, the personalized 1340GT face plates came out very nice. Look forward to you getting everything installed and up and running. David always does some amazing machining work, but he is a hard task manager and is pushing the limits of his machines. All this is very helpful for others, appreciat the time and effort you have gone through.
 
mksj said:
David always does some amazing machining work, but he is a hard task manager and is pushing the limits of his machines.
Click to expand...
Thanks Mark. If you think I push the limits of the metal working equipment, you should see what I do with my woodworking gear. LOL

Just a quick follow-up to add that my point isn’t to dis the PM935, but simply to point out that users should not expect it to be as rigid as a machine twice its weight, and that there are benchtop mills that match or exceed its rigidity. My guess is that the PM833 is a pretty stout machine, and although it has a smaller work envelop (compared to the 935) it has a more contemporary head design.
 
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