How Are You Mounting Your Pm1340gt Lathe?

HA HA its just a saying, but glad there is some good progress made here. I am working to try to have a cast iron base as an option for the machine, but striking out so far. (It can be done, but not at a reasonable price, yet anyway) But we will see what happens. There is always room for improvement, just a matter of if people can realize the difference, and if they are willing to pay the extra cost for it.

Looking at the 1340GT Lathe base though, I think that Rios method of leveling helped a great deal, I think that the shake he had was coming from that mounting bar on the bottom being right in the middle, it seems to flex there.

For example, Our PM-25MV is completely different than the similar sized machine that Grizzly has, and every single day I get calls and emails telling me that Grizzly has a lower price. It has different castings of a much better design, different motor, different drive, so much different on it. But every day, people insist that they are the same exact machine and that I need to match their price. A lot of people do see it, but a lot of them don't.

But if/when the cast base for this 1340GT is available, you guys will be the first to know.

I might be interested in a cast base Matt. Please put me on your "first to know" list.

wrmiller said:

I might be interested in a cast base Matt. Please put me on your "first to know" list.

Click to expand...

Yes... put me on the list too....
I am looking at the cavity at the lower base section Mark mentioned... possibly welding seams and installing some "warmed up" lead maybe?

Mass loading with cement or sand is easy and cheap, or welding some 1/2" plate to the bottom and possibly the top. The next step up would be to have cast iron cabinet shells which have both mass and inherent dampening capacity. Many manufactures like the G4003G no longer offer this option in some of their machine bases for this size lathe. A full cast iron base would probably be almost as heavy as the lathe, seems like a point of diminishing return, as it has not been demonstrated that the machine's turning capacity is affected. As previously mentioned, you can always find a vibration node of a system, add all the rigidity you want but in larger systems something else will break the more rigid it becomes. This is a bigger issue with VFD/adjustable speed systems, doesn't matter how big or small. I have read postings on Grizzly machines and other brands that have had similar cabinet deflection, usually solved by some steel or adding base ballast and/or securing to the foundation.
http://bbs.homeshopmachinist.net/archive/index.php/t-64738.html
http://www.hobby-machinist.com/thre...t-as-described-should-i-send-this-back.28513/

There is a lot of good information at this point, most of which points to some deflection in the cabinet bases. Rio's solution was found after a lot of sweat and frustration, Kudos to Rio. It is a relatively simple solution, other individuals have weighted down the base bottoms and have had similar improvement in their machine stability. So for individuals already with machines, get some sandbags and put them on the lower shelf. According to someone else, about 200lb in the motor cabinet and 100lb in the tailstock end cabinet had a significant improvement in stability. I have seen this mentioned many times for this size lathe, long before I had my PM1340GT. Bigger machines often have cast iron bases and the motor is down low in the cabinet, I was leveling a 1 ton lathe the other day (not bolted down to the foundation), all cast iron massive base and even they are not dead smooth at all speeds. It took a good 1/2 hour to get the ways true to better than 0.00025"/ft over their full span. Getting the machine accurately leveled at multiple points along the bed (getting the twist out) and stable to the foundation is the first thing to do with setting up the machine, then if needed any adjustment to the headstock, and then once the tailstock is centered checking the turning at different points. The two ring test on this size machine is often done with something like a 1.25" bar, sometimes with rings added. If your chuck is not dead true, or the jaws skew the rod, then the test will not be valid. Anything beyond maybe 8" would most likely be supported by the tailstock, which greatly diminishes the affect of the headstock alignment and bed twist affect.

Fascinating post on the affect of inducing bed twist on a 16x40 lathe and measuring the change in the turning and the affect of the tailstock "Without the tailstock: Using the same shaft, just backing off the tailstock center, with the indicator about 2.5 feet from the spindle, I could get plus or minus 5 thou deflection on the indicator by adjusting the leveling bolt. Of note, I could quite reliably get the tailstock back to level just by bringing the indicator back to zero. Of course it helps knowing where it started from...... Bottom line, when using the tailstock, leveling makes very little difference. The tailstock centering however makes a huge difference. Without the tailstock, I could get about 2 thou per foot taper (4 thou on diameter). The numbers will be different of course for every machine." :
http://www.chaski.org/homemachinist/viewtopic.php?f=42&t=92674

Bedtime reading:
http://www.armurerieduroi.com/pages/lathe/lathe_leveling.html#1
http://www.wswells.com/data/howto/H-3.pdf
http://www.neme-s.org/Model_Engineer_Files/Align1.pdf

I'm sure I got to overthinking, yet again. Had my 1340 mounted on Mason pads & all was fine (as far as I was concerned anyway) until I tried the palm-slap-shake-test I got to reading about in this thread. Seemed like I should get some TECOs to better support my lathe & presumably remove what shake I could perceive with the obviously scientific testing method employed. Ordered some from McMaster-Carr & crawled around in the chip & oil debris that found it's way behind & under the machine, got all the legs replaced, re-leveled & tightened down, & lo & behold, now there's more perceived shake than ever. Very noticeable at a few speeds (obvious harmonics) with or without any chuck attached. Loaded up the cabinets with about 400 lbs of bullets on the headstock side & another couple hundred on the tail. Not a lot of difference. Decided to just try a 2x2 piece of square tubing with wooden door shims, (rather than try all the work of drilling & tapping the cabinet as RIO did, at least not yet), & it made quite a difference in the magnitude of the vibrations.
As I said in the beginning, I have been way overthinking all this. I've had no trouble with finish or chatter issues (that weren't my fault) since I started using this lathe, so why didn't I just leave well enough alone? I'm going to figure that just for me, I'm better off back where I started. More crawling, & replacing & leveling, but hey, what else do I have to do after dinner on a rainy night anyway? I'm going to figure also that like my rifles, each of these machines is liable to have it's own likes & dislikes & little quirks here & there. For what it's capable of, & the price I paid, I'm still quite happy with it.

OK, a pic of my super custom vibe damper doo-dad

I have my lathe on the Tecos that Mike (zmotorsports) recommended. Never bothered to check before, but after reading through some of this thread I went out and 'smacked' the headstock on my lathe. The light and DRO vibrated, because they are on flimsy mounts. If the headstock vibrated, I couldn't tell. I did get a sore hand out of it.

But I can hold very tight tolerances and get good finishes, so I'm not going to worry about it. I have noticed an occasional resonance vibration at certain rpms, but given that I'm swinging a very heavy set-tru chuck I'm not surprised nor alarmed. I just use my VFD to shift the rpms up or down a little bit to get rid of the resonance.

The best bang for your buck if you are having shimmy and shake issues with your lathe is to stiffen up the top and bottom mounting plates on each sheet metal column. The current design uses two 1/4" thick plates that are welded on 3 edges with the 4th edge unsupported. The lathe is mounted on the unsupported edge causing the plate to flex under load. Adding plate to only one end of the column will have minimal affect as they both can flex as designed. An alternate solution would be to add plate to the top of both columns and move the leveling feet on the headstock column to the corners (requires 4 leveling feet) where the current mount plate is the stiffest. I would not remove the center stiffener sheet metal piece unless you tie the columns together either by using a one piece top plate as Rio did or a one piece bottom plate.

In my case I also did not notice the ringing until Rio's video pointed it out but did have a shimmy/shake at certain RPM's that I traced to the flex in the stand. I tried adding plates to only the bottom of the columns (from plates I had on hand from another lathe) and this did not remove the shake/shimmy. Rio saw similar results adding his plate only to the top and only saw success when he stabilized both ends of the column.

Best solution if you have the ability to fabricate and weld is to order a lathe without the stand and use that money to build a better stand. You could then use the dead space as storage. I like the look of the factory stand but it has little usable storage.

RIO said:

Mark, your advice and information never fails to help.
You have to watch what you tell me though, like "I would add a Marathon E467". Next thing you know, it's on my machine. So, the same with pouring the stands full of concrete......stand by for pictures...

I think the main thing I am hearing from Matt is BOLT THE STAND DOWN, AND IT MAKES A HUGE DIFFERENCE. Unfortunately, I absolutely can't drill my concrete, unless I like playing Russian roulette with likely hitting a radiant heat water line that's buried in the floor. Otherwise, if you are having instability issues, I absolutely would do that next......in addition to pouring the stands full of concrete

Click to expand...

Total noob to the site, but not to this problem. If you want to drill the concrete floor without hitting a radiant tube, get an IR camera. Should be able to find a home inspector locally - or call an industrial inspection company. You turn up the heat and they can shoot the floor and map out your tubes. Should be able to pinpoint the tubes to within 1/2" +/-. So if you've got 3/8" OD tubes they can get you 1-3/8" stripes on the floor in 10-15 minutes, including a coffee break.

I know most insulation inspectors or "home efficiency" inspectors would have one of the cheap cameras and probably wouldn't charge much. If you drop the coin to have your house shot - which is dead useful for heat loss - they'll shoot your floor while they're at it.

Heck, if you were local to me I'd bring mine over from work and do it for a cup of coffee and a BS session.

Regards,
Ralph