Threading 4140 troubles

You are getting flex/movement and chatter, and it is independent of cutting or threading. When you turned down the center, you should be getting a clean shiny cut. As mentioned 4140 needs a deeper cut and a higher feed when turning, otherwise it will look ragged. Check the insert height. I will also reiterate that if you are turning down stock that small or threading, anything over 1" would need to be supported (rule of thumb is 3-4X the diameter, but on small stuff it will just flex and chatter. I would try threading 1" stock and see if you have the same issue. Below is larger diameter 4140HR and the first half the feed was 0.004"/R and then I doubled it and you can see the finish change. I also do not agree that you need as high as SFM, I usually use 50% of what is indicated on the insert box on my 1T lathe and do just fine. I would first work out getting a good finish on 4140/metal just turning it down, and see if you can get a decent finish, then work on the threading.

20190308_154152.jpg

Small diameter turning and threading with O1, I do support the longer threading with a live center. I use a 5C collet for this type of work, as there is too much movement of the rod with a 3J when doing small diameter work.
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Ischgl99 said:
That view looks better.

For turning, carbide definitely likes fast speeds. For that diameter stock, I would be in the 1200+ range with the inserts I have. I use TNMC inserts for external threading, they are on edge style, but seem to work fine in the 200-300 rpm range. I started with the Arthur Warner HSS inserts mentioned earlier and recently switched to carbide since the holder I bought came with one, and it seemed to worked at the lower speeds as well, but did improve a bit more as the speeds got higher. You could try going faster, if your reflexes can keep up, and see if that helps. It could also be the insert from the kit, I’m assuming the insert is from the kit you posted earlier, is not that good and a name brand insert would work better.

If you have some larger diameter stock you can try on, that will give you a higher SFM without speeding up the machine to the point you can’t keep up and you will see if the higher surface speed helps.
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I tried again just now before class. I ran at 100 rpm and once I got to .030 I started increasing by only .003. Then after 40 I started increasing by .002. It still chipped and tore the threads in the high .040 thousandths. So for ****s and giggle I bumped it up to 1200 and ran it at .005 doc and it seems to clean it up. I did it again and all the sudden it completely tore out all my threads. Idk why it’s not working. I need to try hss and if that doesn’t work then I know it’s something I’m doing. I will be attempting that now.
 
mksj said:
You are getting flex/movement and chatter, and it is independent of cutting or threading. When you turned down the center, you should be getting a clean shiny cut. As mentioned 4140 needs a deeper cut and a higher feed when turning, otherwise it will look ragged. Check the insert height. I will also reiterate that if you are turning down stock that small or threading, anything over 1" would need to be supported (rule of thumb is 3-4X the diameter, but on small stuff it will just flex and chatter. I would try threading 1" stock and see if you have the same issue. Below is larger diameter 4140HR and the first half the feed was 0.004"/R and then I doubled it and you can see the finish change. I also do not agree that you need as high as SFM, I usually use 50% of what is indicated on the insert box on my 1T lathe and do just fine. I would first work out getting a good finish on 4140/metal just turning it down, and see if you can get a decent finish, then work on the threading.

View attachment 437847

Small diameter turning and threading with O1, I do support the longer threading with a live center. I use a 5C collet for this type of work, as there is too much movement of the rod with a 3J when doing small diameter work.
View attachment 437848
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I can’t afford expensive inserts unfortunately. I spend a lot of money on precision Mathew’s tooling and regret it. I will attempt all of this right now. I will say I’m using a 3 jaw and I’m getting about 2-3 thousandths runout on the stock, but I have always threaded with my 3 jaw and been fine. Is this material just a different animal and need a collet or a 4 Jaw and to be indicated to be running completely concentrically?
 
Probably need a collet chuck, it will flex in that diameter. The 4140 is very springy and difficult to get a good cut unless cutting hard, I recently had a lot of chatter with it when I was doing some grooving and not pushing the cutter hard enough, but with that you also can get more flex. A Carmex laydown insert (AG60 with BMA Coating) can be bought as a single insert and they range from $12-20, I have been using the same insert for years, and finally using the 3rd cutting edge on mine. They rarely wear out.
 
mksj said:
Probably need a collet chuck, it will flex in that diameter. The 4140 is very springy and difficult to get a good cut unless cutting hard, I recently had a lot of chatter with it when I was doing some grooving and not pushing the cutter hard enough, but with that you also can get more flex. A Carmex laydown insert (AG60 with BMA Coating) can be bought as a single insert and they range from $12-20, I have been using the same insert for years, and finally using the 3rd cutting edge on mine. They rarely wear out.
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I just ran through every rpm and every feed. I used multiple tools that came with the pm turning and boring kit, it has ccmg inserts. The best finish was no better than any of the pictures shown. I’m in the 3j chuck because I only have a 3j and 4j. I used a live center and I can see the stock wobbling. I’m scared to invest in a collet for this lathe because there is alot of play and looseness. I know it’s alot to do with me being inexperienced. Should I invest in a collet and see if it helps?

I don’t have any larger diameter stock at the moment.
 
I just recalled someone posting a similar problem before, I think the problem ended up being a burr or something like that on the underside of the compound where it meets the cross slide that prevented it from having a rigid fit. If you haven’t checked that, it might be worth a look.

I’m with Mark on this, something appears to be flexing and causing the chatter, but you are also getting close to the point where a different anvil with a larger angle is recommended. You might be rubbing on the thread flanks when you get to the point it starts chattering. I would recommend finding a larger diameter piece of steel and try threading at a larger diameter, at least 1”. If that works, turn it down a bit smaller and keep repeating until you get to your 5/8” thread. If it works at the larger diameters and stops working at 5/8”, then it might need a change to a different anvil for stock that size. The Carmex document I shared earlier has the chart showing what to use, I don’t know if all inserts require a different anvil at the same diameter, or it is dependent on manufacturer, but it’s a starting point.
 
If you are only having this problem with the specific 4140 material you are using then it may have to do with the material. I would try with larger diameter stock and other types of metals, if you do not have a problem then it suggests it is the material and also rigidity. A collet chuck is worthwhile for smaller diameter work, but you will still have issues with flex. When I used my 3J scroll for smaller work it would often flex and try to push between the jaws, mostly for stock under 1/2". Most 4J chucks have fairly coarse holding jaws so work for larger diameter work holding. There are two types of collet systems usually used on smaller lathes, 5C and ER40. David Best wrote a review on the pros and cons on each and should be posted in the forum or you can send him a message. I would not run out and get a collet chuck, unless you plan to do a lot of turning/threading of smaller stock. The PM ER40 and 5C set-true chucks with a D1-4 mount are quite decent, the collets sets are also costly. You seem to have gotten the 1236 at a low point in their production QC, the pictures you show are pretty bad as to the machining/scraping of the carriage as well as other QC issues. I had some similar issue on a Chinese mill I ought from a different vendor and was quite disappointed, it was not a cheap mill.

I use the Carmex AG60 inserts within the range of 8-48 TPI using the same anvil, but it is also a function of the diameter of the work. I am using Carmex holders.
www.hobby-machinist.com

Which 3 Jaw Chuck and collet chuck for incoming PM1340GT

No offense on the picture, I thought it was a bit of humor, but then I may not know what it relates too. We all start out at that level and then learn along the way. To do a basic VFD install for this lathe will run around $600-700 inclusive of the VFD (WJ200-15SF), enclosure, braking resistor...
www.hobby-machinist.com www.hobby-machinist.com
 
mksj said:
If you are only having this problem with the specific 4140 material you are using then it may have to do with the material. I would try with larger diameter stock and other types of metals, if you do not have a problem then it suggests it is the material and also rigidity. A collet chuck is worthwhile for smaller diameter work, but you will still have issues with flex. When I used my 3J scroll for smaller work it would often flex and try to push between the jaws, mostly for stock under 1/2". Most 4J chucks have fairly coarse holding jaws so work for larger diameter work holding. There are two types of collet systems usually used on smaller lathes, 5C and ER40. David Best wrote a review on the pros and cons on each and should be posted in the forum or you can send him a message. I would not run out and get a collet chuck, unless you plan to do a lot of turning/threading of smaller stock. The PM ER40 and 5C set-true chucks with a D1-4 mount are quite decent, the collets sets are also costly. You seem to have gotten the 1236 at a low point in their production QC, the pictures you show are pretty bad as to the machining/scraping of the carriage as well as other QC issues. I had some similar issue on a Chinese mill I ought from a different vendor and was quite disappointed, it was not a cheap mill.

I use the Carmex AG60 inserts within the range of 8-48 TPI using the same anvil, but it is also a function of the diameter of the work. I am using Carmex holders.
www.hobby-machinist.com

Which 3 Jaw Chuck and collet chuck for incoming PM1340GT

No offense on the picture, I thought it was a bit of humor, but then I may not know what it relates too. We all start out at that level and then learn along the way. To do a basic VFD install for this lathe will run around $600-700 inclusive of the VFD (WJ200-15SF), enclosure, braking resistor...
www.hobby-machinist.com www.hobby-machinist.com
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Ok, I’m pretty devastated right now. I have been able to do everything with stainless aluminum and brass ok threading wise. This machine the more I look into it and learn about running a lathe I find more and more problems with it. It’s complete trash considering I was told it would be able to hand any material I threw at it, just maybe not at the doc of a larger machine, but then I was told you probably should buy a Taiwanese machine cause it will last longer doing it that way . I can’t believe I spent 6000 on it. I know after this post it looks like I know nothing, but before this I felt like I was starting to get pretty good for an amateur, threading all other materials has been ok and has worked, turning any material has never looked like the pictures on here and that’s with hss, carbide, and every single speed and feed possible. It’s all material that the finish looks horrible btw. Threading has worked, but nothing ever looks like what other people accomplish.

Give it to me straight though, is this just because I don’t know what I’m doing, or because this machine flat out can’t do what I want? I’m starting to believe that’s the case.

I will buy nicer inserts like you suggested and give that a shot.

Sorry you had the same experience with the mill. It’s a horrible feeling to be told something by a company that has good reviews and then get trash and them just tell you the quality is how they are. The quality I got is not at all what I saw and heard about on this forum before purchasing, or from their employees. There are more things I’m finding about looseness in this machine as I’m putting a dial indicator in every single surface.
 
Ischgl99 said:
I just recalled someone posting a similar problem before, I think the problem ended up being a burr or something like that on the underside of the compound where it meets the cross slide that prevented it from having a rigid fit. If you haven’t checked that, it might be worth a look.

I’m with Mark on this, something appears to be flexing and causing the chatter, but you are also getting close to the point where a different anvil with a larger angle is recommended. You might be rubbing on the thread flanks when you get to the point it starts chattering. I would recommend finding a larger diameter piece of steel and try threading at a larger diameter, at least 1”. If that works, turn it down a bit smaller and keep repeating until you get to your 5/8” thread. If it works at the larger diameters and stops working at 5/8”, then it might need a change to a different anvil for stock that size. The Carmex document I shared earlier has the chart showing what to use, I don’t know if all inserts require a different anvil at the same diameter, or it is dependent on manufacturer, but it’s a starting point.
Click to expand...
Go back and look at my compound and cross slide underneath on page 5. There are .030 deep gouges and different thickness from one side to another. I have never been able to achieve satisfactory finishes like people Do on this forum. I have threaded 303, 304, 6061, and mild steel many times, all with hss. This machine has never achieved nice finishes though. Aluminum is ok, but not like what other people are capable of.

The removable part of the ways and where the teeth are above the lead screw that drive the saddle, when I hit the removable part near the head of the machine it makes the saddle move .002. If I’m hand cranking the saddle up and I go slows near that spot, the hand crank physically gets stuck because the set of teeth attached to the removable part of the ways is not lined up. There are so many issues that I’m starting to learn about and identify that this thing won’t be able to handle most of what I want to do. This is just one of many many examples.

This picture shows what I’m speaking of. I have it all taken apart to try and fix it, but i didn’t try anything other than taking it apart and trying to adjust it.

Sorry for the pity party, but It’s sinking in that this thing may never be capable of making awesome work like what you guys have posted earlier in the thread.
 

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If you remove your tool post from the compound what does it look like? Can you take a close up picture where the bolt attaches? I want to see the region around where the bolt attaches. Does the bolt attach to a tee nut or the compound? Either way, a close up photo would help. Is the region near the threads flat with the compound or pulled up a little? The tiniest of burs or uplifting can give a lot of grief, especially under heavy load. Sorry if I have asked this before. If I have, my apologies.
 
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