I made sure both surfaces were clean and I checked the runout which was less that one thou.
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New PM-1236T Lathe has arrived
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This is my first time setting up a new lathe, so I am still figuring out what to measure and why. But I know for certain it is turning tapers and making rough cuts. I measured taper on parts of only a couple of inches long. And I did have the cross slide and compound locked down. And thanks for bringing that up. I did not do any kind of long run in. I followed the start up procedure in the manual. I did make sure the oil level was correct in the headstock and the apron. And I oiled the change gears and all the oil points. I also greased the gears in the drive end. As for the gibs, I have them adjusted by feel. l keep the compound pretty tight and locked down when cutting.
That is a half thou gage sweeping a rough surface. I cut it at a coarse feed rate with a small radius carbide cutter to accent the toolmarks. But the toolmarks should be uniform. Instead I see variation in the depth of cut. And I did measure more than 2 thou of play in the spindle when I wiggle the test bar. I don't think it is the entire headstock wiggling. But I don't find any axial play, so I am hesitant to tighten up the spindle bearings. I'm a little out of my depth here. I'll do some more tests tomorrow.
Here is what I think is the accurate way to measure spindle play. This is done with the indicator base on the top of the headstock. I had done it this way a couple of weeks ago and I determined there is no play in the spindle. This confirms that. Tomorrow I will tighten up the carriage gibs and see if the surface finish improves.
I'm confused as to what is causing deflection here. And I did check the headstock bolts tight. Maybe I'm twisting the whole lathe bed when I pull on the collet.
I'm confused as to what is causing deflection here. And I did check the headstock bolts tight. Maybe I'm twisting the whole lathe bed when I pull on the collet.
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Not really, the general rule is to not to have a stick out of more than 4-5X the diameter of the rod, the 5X is for more rigid machines. You do not describe the cutter you are using, but the DOC is a function of the nose radius and cutting edge profile/rake/edge, too shallow a depth/incorrect feed rate and you will get a finish like you have. My experience with with 5C collets, which is my primary used chuck is that they do not hold stock very rigid and they are prone to skew the work due to the nature of the 5C collet. I would use a standard chuck or an ER collet chuck. If you want to do light cuts and longer stock unsupported. I would use a larger diameter rod stock like aluminum and use a sharp cutting tool HSS or ground edge insert with the feed set appropriately for the material, and/or do a two collar test. You cannot cut a 1" steel bar out to 9" unsupported, it will deflect and the finish will be bad no matter what the material.
Do not induce bed twist in a new machine to compensate for other factors that are causing your problems. The first thing I would recommend is check the headstock alignment, as just about every 1236T/1340GT I have encountered was out of alignment, and most individuals were trying to twist the bed to compensate. Get a MT5 precision test bar or use Rollie's Dad's Lathe Headstock Alignment Method which works very well, and then you can do the two collar test. Be aware that lathes/work will flex, and the cutter DOC you read on a DRO/Dial will often be slightly off from what you measure. So even if you tail stock is perfectly aligned, you may have to do very small adjustment to get accuracy in the sub 0.001" range on work supported with the tail stock.
Lots of previous threads on this subject:
Taper on a new lathe during a normal turn.
Hello every one. Got a question for the group. I just got my new lathe in finally and getting it all set up. After doing some measurements, what is an acceptable taper from tailstock to head stock on a normal turn, say.....along a 12" turn? Thanks
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A head scratcher here …
I have an interesting issue with my PM-1340GT that I am trying to figure out. I put a 2”x12" bar in the chuck and performed a collar alignment test (with no tailstock). Took light cuts (.002") -- I then put a .0001" indicator on the carriage and ran the indicator over both collars -- I am off...
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- Oct 7, 2020
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Mark, Thanks for the info and the Rollie's Dad's Lathe Headstock document.
I have yet to even check mine..... I did level the lathe with a precision level when I first set it up and then again, a couple month later. The only other thing that I have done was installed a dead center in both the spindle and the tail stock, ran them up close together with an old feeler gauge in between the two centers and adjusted the tail stock so the feeler gauge was square.
I have yet to even check mine..... I did level the lathe with a precision level when I first set it up and then again, a couple month later. The only other thing that I have done was installed a dead center in both the spindle and the tail stock, ran them up close together with an old feeler gauge in between the two centers and adjusted the tail stock so the feeler gauge was square.
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- 2,079
Don't forget - a skim cut is always helpful. Except when it isn't.
Thanks mksj for the advice and the links which I have read and will read again. I have ordered the MT5 test bar and will report back here with my results.Not really, the general rule is to not to have a stick out of more than 4-5X the diameter of the rod, the 5X is for more rigid machines. You do not describe the cutter you are using, but the DOC is a function of the nose radius and cutting edge profile/rake/edge, too shallow a depth/incorrect feed rate and you will get a finish like you have. My experience with with 5C collets, which is my primary used chuck is that they do not hold stock very rigid and they are prone to skew the work due to the nature of the 5C collet. I would use a standard chuck or an ER collet chuck. If you want to do light cuts and longer stock unsupported. I would use a larger diameter rod stock like aluminum and use a sharp cutting tool HSS or ground edge insert with the feed set appropriately for the material, and/or do a two collar test. You cannot cut a 1" steel bar out to 9" unsupported, it will deflect and the finish will be bad no matter what the material.
Do not induce bed twist in a new machine to compensate for other factors that are causing your problems. The first thing I would recommend is check the headstock alignment, as just about every 1236T/1340GT I have encountered was out of alignment, and most individuals were trying to twist the bed to compensate. Get a MT5 precision test bar or use Rollie's Dad's Lathe Headstock Alignment Method which works very well, and then you can do the two collar test. Be aware that lathes/work will flex, and the cutter DOC you read on a DRO/Dial will often be slightly off from what you measure. So even if you tail stock is perfectly aligned, you may have to do very small adjustment to get accuracy in the sub 0.001" range on work supported with the tail stock.
Lots of previous threads on this subject:
Taper on a new lathe during a normal turn.
Hello every one. Got a question for the group. I just got my new lathe in finally and getting it all set up. After doing some measurements, what is an acceptable taper from tailstock to head stock on a normal turn, say.....along a 12" turn? ThanksA head scratcher here …
I have an interesting issue with my PM-1340GT that I am trying to figure out. I put a 2”x12" bar in the chuck and performed a collar alignment test (with no tailstock). Took light cuts (.002") -- I then put a .0001" indicator on the carriage and ran the indicator over both collars -- I am off...