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12x36 belt drive import expectations for depth/width of cut

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  • 12x36 belt drive import expectations for depth/width of cut

    Hi all. I'm starting to get serious about the setup and troubleshooting of my 1983 Enco 12" belt drive lathe I purchased a few years ago. I recently pulled the spindle and jackshaft to change to an appropriate belt length to allow me to use speeds over 500rpm. Doing so resulted in a clearly evident lack of power from the PO supplied 3/4HP cap start only motor. I recently fitted a 2HP 3 phase motor and VFD, which was a nice project and a good success, but I've discovered my capability not really increased as I'm getting very quick and noticeable chatter/vibration on parting with a 2mm wide insert tool or taking a turning DOC of 0.050" off the radius or more. At slower speeds with HSS previously I've had pretty good luck taking 0.050" off the radius and even 0.100" on good material.

    I don't yet want to turn this into a thread looking for suggestions as I've read a ton on this topic and have only started taking actions down the correct path. The supplied stand is not bolted to the floor and as such I can't do a proper "leveling"/de-twisting as the lathe is not heavy enough. My next step is to bolt the stand down, fill it with sand or concrete, and properly setup the lathe. I'm expecting a pretty massive improvement with that effort.

    I'm just looking for a sanity check at this point about what I should expect from this lathe. It seems to me I should be able to run the described cuts even with carbide insert tools (CNMG and CCMT). Can anyone with a similar lathe comment? And maybe include the details on your stand.

  • #2
    Parting is a form of art on my worn-out and under engineered 11x24 Kerry, but it works 95% of the time with some tricks. I use fastest 1500rpm gearing for anything under 1.5"

    You didn't mention what kind of feed/speed/diameter combinations you have tried with or without success?

    Try 1" steel bar no more than 2" out of the chuck, maximum rpm, 2mm depth of cut and 0.3mm per rev feed.
    Its pretty normal to get some chatter on small lathes if you are not feeding the tool enough fast, keep it loaded and its happy.
    This is example of 1.5hp 11x24" lathe maxed out pretty much to 150%
    https://youtu.be/bnHTy6apYIU?t=6
    Location: Helsinki, Finland, Europe

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    • #3
      I'd suggest putting he lathe on a very heavy old shop desk. You'll gain drawers, levelers & weight also room on top. I'm talking about those old dark gray heavy duty industrial ones, I think steelcase made a bunch. When you find them they are usually dirt cheap. I have 4 in the shop.

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      • #4
        MattiJ, most recent experimenting was with 1.375" 12L14 in a 4-jaw with less than 2.5" out of the chuck. The chuck seems to be almost brand new and grips very tightly. Light facing cuts and turning cuts under 0.025" are pretty fantastic at any speed in this material. Similar issues on some larger heavier wall tubing that turned, finished, and threaded very nice with lighter cuts.

        I'm aware of the need to not baby carbide so I've tried power feed from 0.003"/rev to .008"/rev or so on parting and turning and still the same harmonics get excited, even varying the speed from 600-1000rpm. I've even been pretty ham fisted manually feeding to try to break past it, but it's definitely chatter and not rubbing. I really think at the new higher speeds I'm just hitting the resonant frequencies of the lathe and stand. The whole thing just seems to turn into a speaker and the finish is horrible.
        Last edited by JCByrd24; 03-22-2018, 11:16 AM.

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        • #5
          Originally posted by flylo View Post
          I'd suggest putting he lathe on a very heavy old shop desk. You'll gain drawers, levelers & weight also room on top. I'm talking about those old dark gray heavy duty industrial ones, I think steelcase made a bunch. When you find them they are usually dirt cheap. I have 4 in the shop.
          And they weigh about 800 lbs. lol!

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          • #6
            Originally posted by Tundra Twin Track View Post
            And they weigh about 800 lbs. lol!
            That's about what I estimate my stand will weigh when filled with concrete....the stand is useless for storage anyway and concrete is cheap so I figured it was worth a try. I've seen a lot of people with scratch made concrete stands that say they transformed their lathe, that's what I'm looking for!

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            • #7
              Use the desk with a concrete slab poured on it with anchor bolts. Best of both worlds.
              Be sure to build it in it's permanent home. You won't be moving it.

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              • #8
                A photo could help, or at least generate more interest.

                Have you tried using an indicator on various planes and surfaces while cutting to try and localize the primary area of vibration/deflection?

                In so many of these threads the OP disappears and we never hear whether they found a solution.

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                • #9
                  I have the gear drive version of the 12x36 and assume its rigidity is similar to your belt drive?

                  IMHO the cross slide is the weak link in the 12x36. It's just not that massive. The best you can do is take up the slop in the gibs and in the thrust bearing.

                  For everyday turning with carbide I will take off 0.025" - 0.030" per pass. Yes that is very conservative, and you can push it a little harder, but overall that seems to be where it wants to run.

                  Parting is challenging, and again I believe the cross slide is the weak link, springing a bit while parting. I part as much as possible on the bandsaw and then use the lathe to clean up the saw cut.

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                  • #10
                    Glug, I have not done any indicating while turning yet. I did indicate my spindle when I re-installed it and it is tight and true and gets warm to the touch within just a few minutes of running. I should do some deflection measuring with an exaggerated tool in an AXA holder. I think if I were to try to measure during the chatter it would just be meaningless needle bouncing wherever I measured.

                    MTNGUN thanks for your info. This was the sort of comparison I was looking for.

                    Interesting you mention the cross slide, I've seen the compound referenced numerous times, and read of people replacing the compound with solid block. I've not seen the cross slide mentioned but have certainly noticed that it as well as the apron as a whole are not as wide and weighty looking as a "real" lathe. In looking at my compound the fit and design seems better than present day offerings. I have the gibs on it tight and I lock it except when needed. It seems to be a fairly solid block and I back it off so the tool isn't hanging out out past the cross slide as well. I'll get a pic of this tonight. I have considering a solid block replacement but the stand will be first.

                    With the tool cutting edge over the cross slide I hadn't guessed the cross slide being an issue, but something to explore for sure. I don't have a lot of backlash and have adjusted the gibs but worth exploring with an indicator. I've also never blued it to check the fit, but again this vintage seems very good compared to some of the current day stuff. The cross slide ways are actually scraped and the overall finish is very good and the lathe shows very little wear.
                    Last edited by JCByrd24; 03-22-2018, 12:40 PM.

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                    • #11
                      The symptoms you describe sound like your spindle bearing preload is too low. Easy to tighten a little and try it.

                      I have a 12x36 belt drive Jet lathe from 1991 that is likely the same machine you have. Mine doesn't have any of the issues you describe; parting is easy with a 2mm carbide insert tool. I usually part steel with this machine at~800 rpm and power cross feed on the lowest setting; it reliably parts with no drama at all, as long as I keep some sort of cutting oil in the groove.
                      My lathe is also on the original steel stand; it works well enough that I haven't bothered to make a heavier base yet.

                      When I got my lathe, the spindle bearing preload was too tight, so I experimented to find the optimum setting. When the preload was too loose, it acted just like you describe.

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                      • #12
                        As it happens my own lathe is a 12x36 belt driven head model and is from the late 80's. So there's a very good chance that we have the same machine but with different name plates on it.

                        When I got mine it came with the little tin box stands and I used it with them. I found it very low so I lifted the whole works up with pieces of 4x4 lumber under the feet of the boxes. But like you're finding I had a lot of chatter and less than ideal performance. Not so much in the depth of cut like you're finding but just chatter and lack of accuracy when doing long parts that came out tapered.

                        When I moved to my new digs I put those old tin box stands in a metal recycling dumpster where they belong and build up larger foot print construction block pedestals and filled them with gravel on the lower courses and concrete with cast in place 1/2" studs to mount the lathe. And it truly did transform it. I can now do parting cuts in a low direct drive speed instead of using back gear and it has proven to hold out the bed twist and it even SOUNDS different. The whole project was a top to bottom success. The pictures are gone thanks to Photobucket's broken promises to the world but I'll upload them to my HSM picture library and post them shortly.

                        You COULD fill the tin box pedestals with concrete but the footprint of them is still very small so I don't feel that you'll get the best performance. I would suggest either a very durable steel or wood or maybe a composite steel AND wood table with sand bags or similar added mass to the table or do the surprisingly cheap construction block stand like I did. The only possible downside to my pedestals is that I can't move the lathe. But that's really not as impossible as it seems. The whole project cost me about $40 for blocks, $10 for a scoop of 3/4 minus gravel, $10 for a bag of portland cement to mix with the gravel and $20 for the all thread rod nuts and washers for the studs. If I did have to move the lathe for any reason I'd simply make a new set of pedestals.

                        The other upside to this construction block stand is that I raised the lathe up again. The spindle axis is now up at around 48" off the floor. A mat in front of the lathe cuts that to 47". It felt odd at first but now it's a total pleasure to work at the lathe. I'm 6' 1" so if you go this route you may want to adjust the final height a touch. It didn't take long to realize that the lathe was way too low before. The new height has worked out superbly. No more leaning over and tired back after longer sessions. The ONLY downside is that any file work I do is a little higher than I'd like. But all other operations are way better in all respects. So right there I would strongly suggest ditching the cheezy tin boxes that came with the lathe. No point in filling them with concrete or anything else if they are still way too short.

                        Another reason given as a disadvantage was the lack of ability to work in behind if I needed to do anything to the lathe. But if I need to do anything that wild I'll simply lift the lathe off with the engine hoist and put it where I can work on it easily then put it back and re-true it after. Which, thanks to the combination of jacking and hold down nuts on the studs, is pretty much a straight forward job now that I've done it the first time.

                        My own lathe has always been able to make wider cuts than you are reporting. But maybe my tin boxes were a little better than your tin boxes. I've also always adjusted my gibs on the cross slide and compound for a slight drag on the cross slide and a little firmer drag on the compound. Plus I'm a fanatic on keeping the cutting edge in tight for a lack of overhang. Along with that you might also check for play in your head stock bearings. The way I did that was to remove the chuck so that's not a possible source of play and bump the MT5 adapter and MT4 dead center into the taper. Then I set up a dial gauge to read the top of the center and lift from below with a lever and fulcrum bar. You should just see movement that is smooth due to flexing. If you are able to get a jump then flex then your head stock bearings need a trifle more preload. But just until the jump is gone and no more. The adjustment for this is two rings at the outfeed end of the spindle.

                        I'm a HSS fan so this may not be a direct comparison. But with a newly sharpened tool and the right speed I can peel off up to 1/4" cuts in mild steel with the chip looking like a ribbon or short sharp curls depending on diameter and other factors. But that's about maximum for the wussy 3/4 HP motor and I can hear it grunting deeply. And if I push the feed a little it will stall the motor or start the belts slipping. 1/8 hogging cuts are not uncommon but mostly my hogging cuts are more in the range of .06 to .09 DOC provided the stock is tough enough and the piece is close to the chuck jaws. If I try it on something sticking out very far then it will flex and start to chatter. But that's the part itself playing on the lathe.
                        Chilliwack BC, Canada

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                        • #13
                          If I were you, I would check the spindle bearings condition and preload. The bearings must have a decent amount of preload or the spindle would vibrate just like you described. I have a geared version of 12x36 lathe and I was able to adjust the preload to my satisfaction.

                          If you go to www.grizzly.com, they have pretty good manuals for most of their machines including 12x36 lathes. I suspect your lathe is mostly similar. My Grizzly lathe spindle has 2 tapered roller bearings. You adjust the preload by moving the rear bearing on the shaft. Just make sure the bearing has a sliding fit on the shaft. In my case it was a press fit and I had to fix that first.

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                          • #14
                            BCRider it was me who requested photos of your concrete stand a couple of weeks ago, thanks again for the quick reply. I'm still on the fence between scratch built and filling the existing cabinets. Agreed that the foot print is small on the existing ones.

                            Lots of comments on the spindle bearings....I'm almost positive it's not that but easy enough to check again and/or draw it down tighter. I cannot exactly recall the fit of race but if that was an issue it would seem to present itself as the nuts being tight but the spindle still having end play. The bearings also wouldn't seem to warm, which mine do. But again easy to check. I'll give it a little bit more of a gronk tonight and give her a run. The other night I let it run for a couple minutes to warm everything up before I started and I had the same issue.
                            Last edited by JCByrd24; 03-22-2018, 01:28 PM.

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                            • #15
                              One more comment on spindle bearings for these lathes (still assuming yours is like mine and BCRider's) - the inner bearing races may be a pretty tight press fit on the spindle, so the lock nuts can feel tight without actually causing much preload. Mine was tight enough that even with the nuts backed off, I had to use a dead blow hammer on the back of the spindle to loosen the preload from it's originally over-tightened condition. This also meant that when re-tightening it to the final position, I had to tighten the nuts quite a bit more than I expected.

                              The spindle bearings in mine do warm up in use now, but have enough preload that it doesn't matter if they're warm or cold. I never have any need to warm up the lathe before cutting.

                              I'll also point out that when experimenting with preload on mine, in the "too loose" condition that caused chatter like you describe, there was still no measurable play in the spindle, the bearings warmed up slightly when running, and the lock nuts felt pretty tight. It just vibrated and chattered with anything but light cuts. I had to just tighten preload a little bit more at a time until the chatter went away.

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