 |
|
| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
| Reply |
|
|
LinkBack | Thread Tools | Display Modes |
|
|
|
#1
Posted to rec.crafts.metalworking
|
|||
|
|||
Thread Cutting
Hello,
First of all, I have an Acra (now Enco?) 9x20 Chinese bench lathe. This lathe was given to me by a friend a few weeks ago and it didn't get much use at all from him. For some reason the thread cutting system seems way off. When I cut one pass (say 16tpi) and measure the light cut with my thread guage, I'm getting closer to a 17tpi cut. When I try to do a 26 tpi pass I get closer to a 28tpi cut. I've checked and rechecked all of the gear combinations listed on the chart and the are correct. Additionally, when I try to use the thread chasing dial, I can never get the same cutting pass. For example, I'll use strictly the number 1 on the dial and my second cutting pass will be right in between the first cutting pass. I'll try it for a third pass and I'll get a whole different cutting pass. This is really frusterating! Has anybody ever heard of this before? I was actually impressed with the quality of this Chinese manufacturing, but now I'm beginning to wonder... If pictures would help at all I'd be glad to take a few and post them. Thank you very much, Carter |
|
#2
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
|
|
#3
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
|
|
#6
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
You guys all had some very good info...
Here's a link to some photos I took earlier: http://pg.photos.yahoo.com/ph/cj1210...548scd&.src=ph Right now trying to get the thread chasing dial working is not my biggest concern. I've got to get an accurate TPI first. For some reason though I think this may be all intertwined... As you can see from the photos I've strictly kept the setting (according to the charts and gears) to 16tpi. The leadscrew is exactly 16tpi (not anything metric as you can see from the picture). When I turn the chuck over one rotation by hand I don't get a complete rotation in the leadscrew. This obviously points to some kind of gear miscalculation on the manufacturer's part... (at least that's the only explanation I can think of at the moment). Now, as far as the thread chasing dial, I've tried pulling it away from the headstock while cutting in order to take all of the play out. This doesn't do anything. I've also tried giving it resistance with the carriage wheel. Maybe the thread chasing dial can't work properly if the gears are messed up. For example maybe when it's set to 16tpi and it's really cutting close to 17tpi this will then proceed to not let the half nut engage at the proper time, which will defeat the whole purpose of the thread chasing dial. There is about .007" play in the leadscrew itself which I can probably fix with a thin washer. There is about .014" play in the half nut unit. This I'll have to pull apart to see if I can tighten it up. This could definitly be part of my problem with not getting the same cut to line up and is just not right, but something tells me there's more to it. Like I said up above I've tried keeping pressure on the carriage (away from the headstock) and it hasn't done any good... Any other ideas!? Thanks, Carter Eric R Snow wrote: On 10 May 2006 14:08:37 -0700, wrote: Hello, First of all, I have an Acra (now Enco?) 9x20 Chinese bench lathe. This lathe was given to me by a friend a few weeks ago and it didn't get much use at all from him. For some reason the thread cutting system seems way off. When I cut one pass (say 16tpi) and measure the light cut with my thread guage, I'm getting closer to a 17tpi cut. When I try to do a 26 tpi pass I get closer to a 28tpi cut. I've checked and rechecked all of the gear combinations listed on the chart and the are correct. Additionally, when I try to use the thread chasing dial, I can never get the same cutting pass. For example, I'll use strictly the number 1 on the dial and my second cutting pass will be right in between the first cutting pass. I'll try it for a third pass and I'll get a whole different cutting pass. This is really frusterating! Has anybody ever heard of this before? I was actually impressed with the quality of this Chinese manufacturing, but now I'm beginning to wonder... If pictures would help at all I'd be glad to take a few and post them. Thank you very much, Carter Greetings Carter, It sounds like it may have a metric leadscrew. Another thing to check when looking at the gears is to see if paired gears are used and if so maybe one of the gears is on the shaft the wrong way. What I mean is this: the lathe may have a 120 tooth gear paired with a 127 tooth gear. These gears will be on the same shaft and both gears will be keyed to the shaft so they rotate together. There should be a gear driving the 120 tooth gear and the 120 tooth gear should drive another in turn. So the 120 tooth gear is acting as an idler. OR, it could be the 127 tooth gear that is acting as the idler. But if the lathe has an inch leadscrew and you want to cut metric threads then one gear will drive the 127 tooth gear, which spins the 120 tooth gear, which drives another gear. This is how the metric conversion is done. Also, when cutting metric threads using this method you must keep the half nut closed until all threading passes have been made. This means that at the end of the cut you must withdraw the tool and stop the lathe at the same time. Then with the tool clear of the part, reverse the spindle to back the tool up, then so on and so forth. If your machine is equipped with a metric leadscrew and the gears are set up for cutting inch threads then the same thing happens. By the way, when you figure out what is really going on please let us know. Eric |
|
#7
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
On 11 May 2006 17:17:56 -0700, wrote:
You guys all had some very good info... Here's a link to some photos I took earlier: http://pg.photos.yahoo.com/ph/cj1210...548scd&.src=ph Right now trying to get the thread chasing dial working is not my biggest concern. I've got to get an accurate TPI first. For some reason though I think this may be all intertwined... As you can see from the photos I've strictly kept the setting (according to the charts and gears) to 16tpi. The leadscrew is exactly 16tpi (not anything metric as you can see from the picture). When I turn the chuck over one rotation by hand I don't get a complete rotation in the leadscrew. This obviously points to some kind of gear miscalculation on the manufacturer's part... (at least that's the only explanation I can think of at the moment). Now, as far as the thread chasing dial, I've tried pulling it away from the headstock while cutting in order to take all of the play out. This doesn't do anything. I've also tried giving it resistance with the carriage wheel. Maybe the thread chasing dial can't work properly if the gears are messed up. For example maybe when it's set to 16tpi and it's really cutting close to 17tpi this will then proceed to not let the half nut engage at the proper time, which will defeat the whole purpose of the thread chasing dial. There is about .007" play in the leadscrew itself which I can probably fix with a thin washer. There is about .014" play in the half nut unit. This I'll have to pull apart to see if I can tighten it up. This could definitly be part of my problem with not getting the same cut to line up and is just not right, but something tells me there's more to it. Like I said up above I've tried keeping pressure on the carriage (away from the headstock) and it hasn't done any good... Any other ideas!? The chart in photo 11 shows the gear box driven from the 127 tooth gear which is being used as an idler gear; but, in photos 6, 7, 8 and 9, the gear box appears to be driven by the 120 tooth gear, which only used for metric threads. Gerry :-)} London, Canada |
|
#8
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
I feel extremely stupid right now... I could have sworn I checked and
rechecked those gears according to the chart 20 times. Thanks for your time guys. I'll go change that right now and then give it another shot... Maybe this will fix my thead chasing dial problem as well. If it doesn't, you know I'll be back! Thanks again, I came to the right place! Best Regards, Carter |
|
#9
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
According to :
You guys all had some very good info... Here's a link to some photos I took earlier: http://pg.photos.yahoo.com/ph/cj1210...548scd&.src=ph These photos do it! Right now trying to get the thread chasing dial working is not my biggest concern. I've got to get an accurate TPI first. For some reason though I think this may be all intertwined... As you can see from the photos I've strictly kept the setting (according to the charts and gears) to 16tpi. The leadscrew is exactly 16tpi (not anything metric as you can see from the picture). When I turn the chuck over one rotation by hand I don't get a complete rotation in the leadscrew. Maybe the leadscrew is not metric, but your gear train is set up for metric. In the photo "b2e3scd.jpg", which shows the entirity of the threading chart, it shows that the input to the gearbox should have its gear engaging the 127 tooth gear for inch thread 'n/1"', and it should engage the 120 tooth gear for the metric thread "mm" And looking at the photo "b1fascd.jpg", it is obvious that the gear from the quick-change gearbox is engaging the 120 tooth gear. So -- you need to loosen the various nut, exchange the spacer and gear on the input shaft to the QC gearbox, and then re-mesh all of the gears and tighten them back in place. When you had initially posted your question, I was thinking that you had the other common pair of gears for metric/inch transpostion, 100/127, which would introduce more error than you were observing. However, with 120/127 you would get (depending on the direction of the transposition) either 15.12 TPI or 16.93 TPI -- the latter being rather close to your observed 17 TPI. This is probably enough all by itself. I presume that the flat paddle lever on the right of the apron is your half nuts engage, and the long round lever in the bottom center of the apron is your power feed, either longitudinal or cross-feed. If you had been using that by mistake, you would have gotten a much greater mismatch. This obviously points to some kind of gear miscalculation on the manufacturer's part... (at least that's the only explanation I can think of at the moment). Nope -- simple mis-positioning of one gear -- you are set up for metric threading. Now, as far as the thread chasing dial, I've tried pulling it away from the headstock while cutting in order to take all of the play out. This doesn't do anything. I've also tried giving it resistance with the carriage wheel. Your thread chasing dial will not work properly for metric threading, even when you *know* that is what you are doing. For it to work properly, you would need to have the leadscrew and half-nuts metric as well. Maybe the thread chasing dial can't work properly if the gears are messed up. For example maybe when it's set to 16tpi and it's really cutting close to 17tpi this will then proceed to not let the half nut engage at the proper time, which will defeat the whole purpose of the thread chasing dial. It truly will not work properly when you are set up for cutting *any* metric threads. There is about .007" play in the leadscrew itself which I can probably fix with a thin washer. Don't worry about it. There is about .014" play in the half nut unit. Again -- don't worry about it. These are normal amounts of play, and since the carriage is always moving in the same direction when cutting, the play is taken out. And especially so if you use the 29.5 degree compound infeed, so the cutting load is always on the left side of the tool. This I'll have to pull apart to see if I can tighten it up. You can't -- and if you could, it would still wear back to that much play rather quickly. This could definitly be part of my problem with not getting the same cut to line up and is just not right, but something tells me there's more to it. Yep -- that one gear in the train before the QC box. Like I said up above I've tried keeping pressure on the carriage (away from the headstock) and it hasn't done any good... Any other ideas!? Yep -- re-set the gears. Then you should be fine. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#10
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
On 12 May 2006 05:23:43 GMT, (DoN. Nichols)
wrote: According to : You guys all had some very good info... Here's a link to some photos I took earlier: http://pg.photos.yahoo.com/ph/cj1210...548scd&.src=ph These photos do it! Right now trying to get the thread chasing dial working is not my biggest concern. I've got to get an accurate TPI first. For some reason though I think this may be all intertwined... As you can see from the photos I've strictly kept the setting (according to the charts and gears) to 16tpi. The leadscrew is exactly 16tpi (not anything metric as you can see from the picture). When I turn the chuck over one rotation by hand I don't get a complete rotation in the leadscrew. Maybe the leadscrew is not metric, but your gear train is set up for metric. In the photo "b2e3scd.jpg", which shows the entirity of the threading chart, it shows that the input to the gearbox should have its gear engaging the 127 tooth gear for inch thread 'n/1"', and it should engage the 120 tooth gear for the metric thread "mm" And looking at the photo "b1fascd.jpg", it is obvious that the gear from the quick-change gearbox is engaging the 120 tooth gear. So -- you need to loosen the various nut, exchange the spacer and gear on the input shaft to the QC gearbox, and then re-mesh all of the gears and tighten them back in place. When you had initially posted your question, I was thinking that you had the other common pair of gears for metric/inch transpostion, 100/127, which would introduce more error than you were observing. However, with 120/127 you would get (depending on the direction of the transposition) either 15.12 TPI or 16.93 TPI -- the latter being rather close to your observed 17 TPI. This is probably enough all by itself. I presume that the flat paddle lever on the right of the apron is your half nuts engage, and the long round lever in the bottom center of the apron is your power feed, either longitudinal or cross-feed. If you had been using that by mistake, you would have gotten a much greater mismatch. This obviously points to some kind of gear miscalculation on the manufacturer's part... (at least that's the only explanation I can think of at the moment). Nope -- simple mis-positioning of one gear -- you are set up for metric threading. Now, as far as the thread chasing dial, I've tried pulling it away from the headstock while cutting in order to take all of the play out. This doesn't do anything. I've also tried giving it resistance with the carriage wheel. Your thread chasing dial will not work properly for metric threading, even when you *know* that is what you are doing. For it to work properly, you would need to have the leadscrew and half-nuts metric as well. Maybe the thread chasing dial can't work properly if the gears are messed up. For example maybe when it's set to 16tpi and it's really cutting close to 17tpi this will then proceed to not let the half nut engage at the proper time, which will defeat the whole purpose of the thread chasing dial. It truly will not work properly when you are set up for cutting *any* metric threads. There is about .007" play in the leadscrew itself which I can probably fix with a thin washer. Don't worry about it. There is about .014" play in the half nut unit. Again -- don't worry about it. These are normal amounts of play, and since the carriage is always moving in the same direction when cutting, the play is taken out. And especially so if you use the 29.5 degree compound infeed, so the cutting load is always on the left side of the tool. This I'll have to pull apart to see if I can tighten it up. You can't -- and if you could, it would still wear back to that much play rather quickly. This could definitly be part of my problem with not getting the same cut to line up and is just not right, but something tells me there's more to it. Yep -- that one gear in the train before the QC box. Like I said up above I've tried keeping pressure on the carriage (away from the headstock) and it hasn't done any good... Any other ideas!? Yep -- re-set the gears. Then you should be fine. Enjoy, DoN. DoN, This business with the 120 and 127 tooth gears was what I had posted. How the gear, either the 120 or 127, was not being used as an idler. I guess I should have made it more clear in my first post. ERS |
|
#11
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
According to Eric R Snow :
On 12 May 2006 05:23:43 GMT, (DoN. Nichols) wrote: [ ... ] Yep -- re-set the gears. Then you should be fine. [ ... ] DoN, This business with the 120 and 127 tooth gears was what I had posted. Yes -- I saw your posting *after* I posted my followup. How the gear, either the 120 or 127, was not being used as an idler. I guess I should have made it more clear in my first post. From the chart, it is expected for the 127 tooth to be the one used as an idler gear. I tend to post a lot more detail, simply because if someone is having problems of this nature, the more detail the better the chance that he can make things work -- and avoid similar problems in the future. One thing which I did *not* get around to mentioning is that he needs to bear in mind that whenever he is cutting metric threads, that he should leave the half-nuts engaged the whole time, and reverse the lathe to get to the start for another pass. This is a side-effect of the threading dial just plain not working with metric threading and an imperial leadscrew (or for that matter, with imperial threading, and a metric leadscrew). I also should mention that this can be a serious pain when cutting threads to a shoulder, unless the lathe has a quick-acting clutch to stop the spindle before there is a crash. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#12
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
From ERS:
Another thing to check when looking at the gears is to see if paired gears are used and if so maybe one of the gears is on the shaft the wrong way. What I mean is this: the lathe may have a 120 tooth gear paired with a 127 tooth gear. From the OP: Here's a link to some photos I took earlier: http://pg.photos.yahoo.com/ph/cj1210...548scd&.src=ph These two gears he's talking about are clearly visible in photo 100_2259. You need to change the small input and output gears on the pair of big gears so that they are both on the same large gear (it doesn't matter which one since it will then be acting as an idler--a gear which transfers power but does not change ratios). I'm guessing there's a spacer under one or both of the small gears, and if you swap one of the gears and its spacer in position on its shaft, and re-align the bracket and the big gears so that everything meshes, you'll be all set... --Glenn Lyford |
|
#13
Posted to rec.crafts.metalworking
|
|||
|
|||
|
Thread Cutting
These two gears he's talking about are clearly visible in photo
100_2259. You need to change the small input and output gears on the pair of big gears so that they are both on the same large gear. Also see pic 100_2252 which shows the "a" and "b" gears both meshing with the 127 tooth gear. That's not how yours are set up... --Glenn Lyford |
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Newbie question on precision thread | Metalworking | |||
| Problem with cutting a thread on my lathe | Metalworking | |||
| Thread cutting (lathe) help! | Metalworking | |||
| Brown's gas?? | Metalworking | |||
| Questions on repairing/replacing damaged thread in aluminum engine head. | Metalworking | |||
Hybrid Mode
