GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: rualert on January 05, 2023, 08:07:06 PM
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Okay all, so I have one of the Sieg 7X14 Mini lathes and it seems that the spindle has about 4 6 thousandths of play. This measured from both the top of the main housing, and the bed ways both. Now my dial indicator is not an expensive one, but it does seem consistent. So I'm turning the breech end of a .257 barrel for my Condor and notice that even though I get it within .002 run out it was cutting oblong rather than correctly circular. So I take the jaws out of the chuck, clean them, and the chuck, then reassemble. Check it before the cleaning and it's 12 thousandths with an aluminum rod. Aftr the cleaning check it again this time using an 1/8 inch drill bit, same result 12 thousandths. So any good ideas? I already tried using an extra fine round shone on the chucks jaws just lightly and when I chucked the barrel up it was almost dead on. Maybe the tool post doesn't have enough rigidity? Going to tear the head stock down this weekend and upgrade the berrings to tapered roller ones and see if that takes a bit more of the play/run out up. Guess I'll order a steel tool post and new holders and adjust the cross slide jibs again just to be sure those are as close as I can get them. I hate having to chop off another 3 inches of barrel to redo that Air Force breech diameter without it ending up oval again. Guess I'll test it with a small piece of aluminum or steel rod and see if it stays circular.
Any and all ideas, input pointers or suggestions are welcome. I value everyones advice here, you have all guided me in the right direction over the years.
Thanks in advance,
Casey
Oh if you happen to read this Mr. Noble, PM me about one of your great 257 valves please.
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That first line should say 4 to 6 thousandths.. Sorry about the fat fingers.
Casey
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Have you checked your current spindle preload?...
Jesse
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cutting oblong?
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I'll check the spindle today or tomorrow. Thanks for the pointer Jesse. Oblong as in oval or out of round where on side of the barrel came out with close to .3 while the other was down to .1 180 degrees across. Is that a better description?
Thank you for the pointers thus far, I'll keep working on it until it's back to dead centered again.
Casey
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Yes, just still not sure how oblong happens unless it’s not cutting on 1 side, what technically we’d call ‘wobble’. Chuck up a piece of scrap and mark it with dykam or sharpie or something and you can get a visual of whether it’s cutting all the way around. Then keep going until all the coating is removed and check to see if it’s still oblong. Even with some wobble, should come out round if you take off enough material, shouldn’t it?
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Thanks for the additional pointers Jon, I would think so, and I'll try you suggestion to try to rule out if it's maybe my cross slide injecting wobble on this barrel. It did take a bit of work to get it chucked up good and minimoize the wctual wobble to essentially gone with the help of a plug at the open end of the spindle to help keep the extra length of barrel from moving around while it was spinning. The things we go through to have a lathe we can afford and won't break through the floor. Next shop will be on a slab and I'll upgrade to an older Bridgeport if I can find one decent for less than 10K.
Casey
I will be checking that spindle preload tomorrow, and before I tear it down for the tapered roller bearing upgrade
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Okay all, so I have one of the Sieg 7X14 Mini lathes and it seems that the spindle has about 4 6 thousandths of play. This measured from both the top of the main housing, and the bed ways both. Now my dial indicator is not an expensive one, but it does seem consistent. So I'm turning the breech end of a .257 barrel for my Condor and notice that even though I get it within .002 run out it was cutting oblong rather than correctly circular. So I take the jaws out of the chuck, clean them, and the chuck, then reassemble. Check it before the cleaning and it's 12 thousandths with an aluminum rod. Aftr the cleaning check it again this time using an 1/8 inch drill bit, same result 12 thousandths. So any good ideas? I already tried using an extra fine round shone on the chucks jaws just lightly and when I chucked the barrel up it was almost dead on. Maybe the tool post doesn't have enough rigidity? Going to tear the head stock down this weekend and upgrade the berrings to tapered roller ones and see if that takes a bit more of the play/run out up. Guess I'll order a steel tool post and new holders and adjust the cross slide jibs again just to be sure those are as close as I can get them. I hate having to chop off another 3 inches of barrel to redo that Air Force breech diameter without it ending up oval again. Guess I'll test it with a small piece of aluminum or steel rod and see if it stays circular.
Any and all ideas, input pointers or suggestions are welcome. I value everyones advice here, you have all guided me in the right direction over the years.
Thanks in advance,
Casey
Oh if you happen to read this Mr. Noble, PM me about one of your great 257 valves please.
After a few years of use my Chinese LatheMaster bench top lathe spindle started having runout issues so I replaced the factory spindle ball bearings with a pair of tapered roller bearings that allows some spindle bearing preload. This "upgrade" solved my runout issues.
Perhaps this may be of interest............
https://www.youtube.com/watch?v=goCNyyNcB80 (https://www.youtube.com/watch?v=goCNyyNcB80)
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Ed, did your runout cause an oblong piece? I’m just having a hard time seeing how oblong can happen, maybe I’m missing something.
Casey, by the time you get this figured out and corrected, you’ll know that machine intimately, which will make you way better at making it do what you want. There may be a Sieg forum somewhere, maybe at groups.io, where you can go from our generic pontificating to people who know that specific machine and it’s peculiarities.
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Ed, did your runout cause an oblong piece? I’m just having a hard time seeing how oblong can happen, maybe I’m missing something.
Casey, by the time you get this figured out and corrected, you’ll know that machine intimately, which will make you way better at making it do what you want. There may be a Sieg forum somewhere, maybe at groups.io, where you can go from our generic pontificating to people who know that specific machine and it’s peculiarities.
The only issues I had was deflection of the work piece due to pressure of the cutting tool along with the noisy head stock bearings. The biggest issue I had cutting unwanted tapers because the tail stock wasn't properly aligned with the head stock. My initial minilathe was a 7x12 Harbor Freight offering that I'm convinced was assembled out of parts failing QC inspections, if there were any in the first place. Here is a pic of that "on sale for $250" HF lathe (bought decades ago) after it was fitted with a 14" bed from The Little Machine Shop.............
(https://i.imgur.com/HWKW2aF.jpg)
Due to the poor tail stock mounting design where the tail stock needed to be removed when aligning the sliding base plate for alignment I ended up drilling and tapping the base casting to add some "jack screws" so the tail stock could be aligned without removing from the bed. Worked better but still a hokey work around. I later bought a bit larger 8x14 LatheMaster which I believe was the same as the HF 8x12 lathe from years back (no longer offered). The LatheMaster was (still is) a better machine but a couple decades ago it cost $450ish dollars when ordered..........
(https://i.imgur.com/BJFXQ1w.jpg)
After a couple years I decided to disassemble the LatheMaster and scrape the ways and dovetails to create closer fitting sliding surfaces since the lathe would chatter with a tiny bit of excess cutting tool depth. I was amazed by how poorly the machined surfaces were fitted with only about 25% contact between the surfaces. This was determined by spread a thin coat of "machinist blue" (I actually used artist oil paint) and transferring the blue from a smaller grade "A" granite surface plate to the machined surfaces. After about a week of bluing/scraping high surfaces/checking blue transfer over and over I got a rather mediocre flatness of about 60% transfer using an old file with a "proper grind" on the end. LOL, that was a LOT of grinding/sharpening with the file dulling rapidly scraping the cast iron surfaces. After the "hack work" the sliding surfaces were considerably smoother and the chattering was reduced considerably. Here are a couple pics of a steel backing plate I made for a new 5" chuck done on the scraped LatheMaster using cheap carbide insert tooling from AliExpress..........
(https://i.imgur.com/tiS1L4U.jpg) (https://i.imgur.com/BF7Kbe5.jpg) (https://i.imgur.com/AAka79v.jpg) (https://i.imgur.com/DjSNEGt.jpg)
I mentioned all this because, as a "seat of the pants machinist with hobby tools" I don't know why or how a part could be accidentally turned onto an "oval" but perhaps some useful info can be found.
https://www.youtube.com/watch?v=T7w84CrBEE8 (https://www.youtube.com/watch?v=T7w84CrBEE8)
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There's a few things that can cause run out, what you need to do is to measure stuff systemically.
If it was me, I'd pull the chuck off, and measure the spindle taper - assuming you have one. I would use a dial test indicator (DTI) for that. That's the type of indicator that has a small lever and ball on the end, not the plunger style. It you don't have one, I'd recommend you get one. You can find a used one or a cheap import. I have an old Enco 0.0005"/div one that works fine. Rotate the spindle by hand and see what kind of run out you have. My mini-lathe, fortunately, was pretty good, under 0.0005", actually closer to 0.0002". If you don't have a machined taper inside the spindle bore, then indicate on the surface of the spindle plate and see what you have. If any of these surfaces have a lot of run out, show your measurement set up and your results. If you have low run out, even when pushing up and down on the spindle, your spindle is good. If the run out changes a lot, your bearings need attention. Could be the preload was never set at the factory, or it loosened in transit, or,... Might trying to very slightly tighten it, and retest. If that doesn't work then it's time to replace the bearings.
If there's very little run out, it is possible that when you mounted the chuck, there was a piece of crud, or stuff, that prevented the chuck from registering properly. Clean the spindle and chuck mating surfaces and reinstall the chuck. Now get your hands on a steel dowel, say 1/2" diameter and chuck it up. These dowels are ground and are a pretty good reference. Make sure your chuck jaws are clean (spotless). Using the DTI, measure the run out of the dowel near the jaws, and at a known distance near the end of the dowel. What do you measure? If everything is clean and properly installed (and the spindle run out is ok) the dowel run out should be low. Possible problems could be worn or bell mouthed chuck jaws. Or your chuck is full of chips and you need to thoroughly clean it out... I have a three jaw that needs cleaning...
Some other things you can check is the run out of the chuck body. It might tell you that the chuck was made poorly, or incorrectly installed.
This is not an exhaustive list, but I hope it helps in a small way to diagnose the issue.
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Thank you all for your input, I'm gong to start by getting one of those dial test indicators and check the spindle and each part of it and the chuck. I have a steel tool post arriving Monday since the current one is one of those aluminum sets I picked up several years back when I got the machine from Frank at Mini-Lathe.com. I'm sure it has a good lack of good rigidity, so that's on the list. I'll get the test dial indicator on the way, and begin pulling the Spindle down, cleaning, and I might just go ahead and replace the current bearings with the set of tapered rollers I have sitting on the bench.
First picture shows what I referred to as “oblong” how about more out of round. I may have been trying to take too much of a cut on each pass. The rest of the barrels 20 inches were hanging out the left side of the spindle and were shaking pretty hard at first. That’s when I made the insert from Delrin and plugged the end of the spindle to support the barrel. Left a few thousand so it didn’t squeal and it seemed a lot better virtually no wobble or shaking but you can see the results.
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How much barrel was sticking out from the chuck when you did the turning? Did you support the barrel? What is the diameter of the barrel? Rough rule is no more than 6X the diameter sticks out from the chuck with out support. You can do more, but you have to worry about deflection. In other words, you can only take very light cuts. Were you using carbide or HSS tooling? Can we see a picture of the tooling and your set up?
What were you trying to do? Set up for an LDC or something else?
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Nevermind about my question on which end you were turning. Reread your first post. Breech end.
Do you have a four jaw chuck? If you do, you can indicate it with the DTI and eliminate any run out. This assumes you have addressed any spindle issues. Three jaw chucks, especially on mini-lathes don't have terrific run out. 4-5 thousandths is possible. I get about 0.003" on my three jaw, if I am lucky.
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I have both HSS and carbide tooling, started with carbide, then switched to HSS but apparently was taking too heavy cuts, and I had about 3 inches of the breech end sticking out. I can part it off and re start with much less and work my way to the 2.5 or so inches I need for the breech. I have both a steel tool post and holders and a dial test indicator showing up tomorrow. So I'll do the testing and shorten up the amount of work hanging out of the chuck. Should have known better with the small lathe, but I'm still an amateur machinist.
I greatly appreciate the input, help and solid advice all of you have provided. I'll get some pictures of the tooling for you still, and the new pieces when they arrive along with keeping this updated then start a fresh thread for the project.
Thank you all again,
Casey
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The other thing to know is the cutting speeds for HSS and carbide are quite different. You need to go about 4 times slower with HSS. Carbide also needs a deeper cut usually than HSS. With HSS you can shave off less than 0.0005" if you want to. Of course it needs to be sharp - like slice your finger sharp, but it's my go to for fine work.
Typically for carbide there is a minimum cut which is on the order of the nose radius of the tool or greater. They don't like to cut at 10% or less than the nose radius depth. If you use a ground insert like a TCGT, you can take finer cuts than say with a TCMT. Only problem with TCGT ground inserts is they tend to chip. If your surface finish looks scratchy and you are using TCGT, your insert has a chip or defect on it. You might have to use 10X magnification to see it, but it the finish is bad, there's a chip and it's time to change the edge. I have sourced carbide inserts from AliExpress. They may not last too long, but they are cheap enough that I don't care much. There's no doubt in my mind that 99% of the inserts sold on AliExpress are counterfeit. However, they last long enough for my limited use.
Had to buy some Kennametal Top Notch threading inserts and they were $10 each, and list for about $24. I was unhappy to spend $50 on 5 inserts, but couldn't find any others that fit my internal threading bar. At $10 each, they are likely counterfeits, but that's what I can afford right now.
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So here's a few pics of the current tooling, please excuse the mess, shop is in disarray. I have been in another state for 3.5 years so I'm just getting beck to it. I have some HSS pieces, decent sized ones and the smaller versions picked up locally that actually hold up pretty well when I grind them right. Small carbide tools, second full set, new boring bars with carbide cutting inserts. The old aluminum tool post, new replacement steel post that arrived today. I went ahead and mounted that, setup the Test Dial Indicator and took a quick measurement on the spindle's mount for the chuck. In the next few days I'll pull the chuck, take more measurements to make sure the spindle in within a decent range. Let me know if the difference in these readings in excessive. Guess I'll go ahead and do the tapered roller bearings on the main spindle too, and see if I can take some of the backlash out of the cross slide and the top slide.
Thanks again everyone,
Casey
(https://i.postimg.cc/28K77ydG/Bsic-Tooling-HSS-and-carbide-01.jpg) (https://postimages.org/)
(https://i.postimg.cc/3r9BWndP/Run-out-reading-01.jpg) (https://postimages.org/)
(https://i.postimg.cc/Nj27Jtpc/Run-out-reading-02.jpg) (https://postimages.org/)
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So, sorry about the long delay, life sometimes gets in the way. None the less, finally pulled my chuck, and checked the spindle's run out with my new little DTI. Thanks for that by the way, I really like that little tool. Found that I only have a coupe thousandths of actual run out on the spindle and since I don't yet have a ton of hours on the machine the bearings (which will still be swapped out for the tapered roller ones I have) are also not an issue yet, nice and tight. I did however find that I apparently, (dumb one on me) apparently the last time I pulled the jaws to clean and lube everything put them back in the wrong places. As in #1 was not in it's proper place and so on. So, I cleaned everything out well, and carefully put the jaws back strarting with #1 in the proper starting slot, then 2 next, and the last where they belong. Now th chuck runout is just 4 thou, and I was able to place a fresh piece of steel rod in the same chuck and carefully tighten it checking run out as I went, and got it to almost nothing just by moving it slightly while tightening and measuring while I did so. It centered up and fell into place. So it seem I screwed it up, but with your help found my mistake.
Thank you to everyone who gave advise, hints, and instructions as to what to check, look for and so on.
I greatly appreciate it,
Casey
P.S. I'll update in a new thread after I get the time to re-cut my barrels breech area to fit my Condor.
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Glad you got it sorted out. Looking forward to your progress.
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I would suggest a practice run with this lathe before you turn a barrel again. Test it's performance on a scrap piece first. This thread is a little hard to follow. Some of the descriptions are vague or questionable. Something doesn't seem right though.
Keep using your machine and keep learning.
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Thanks Bruce and Karl, I did try a spare piece of steel rod about three feet long to simulate the barrel, made a good several cuts, then checked it for roundness and run out. It was virtually nothing so I think I did find the issue as the issue with the barrel was the first time I have even had a piece come out like that, and I had pulled the jaws to clean and check their faces before I cut that barrels breech. So I was to blame, but I'll make a couple more test cuts before I try the barrel again, those are not cheap, and TJ makes a really nice barrel.
Casey
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that's a lot of metal hanging on the outboard side. If it's whipping around you're gonna have trouble. Might need to support that end to maintain any accuracy.
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Thanks for that. I had not thought I might need support on the opposite end. Guess I'll need to make something pretty solid for that.
Casey
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At no time should anything be whipping about. Even a simple board with a strategically located hole in it can be used to keep the outboard piece moving about too much. Either that or reduce your RPM to keep it under control. Stuff moving on one end, can affect the other end.
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If it isn't critical, I'll use delrin round scraps. I bore to the barrel OD, and the delrin OD just fits into the headstock spindle. Of course, you can always just wrap tape around the barrel so it fits tighter in the headstock. Flopping is no bueno.