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Unimat 3 alignment problem?
Hello:
After a long hiatus while waiting for some tools from Asia, I started working on a part to fix my U3's feed screw problem. This is the piece: It is quite small, total length is 35mm.? Large part is ? 20mm x 13mm and the rest is ?12mm x 20mm. It will have a brass centre and will replace the OEM bushing once the feed screw receives a new, longer thread at that end as well as a new handwheel. But I digress ... I used to think I had my U3 properly/reasonably aligned. After a rather long process and using thin shims, I eventually managed to achieve this result: But I have run into a problem: The distance between the points where the readings were taken is ~ 20/21mm. And as you can see, the difference between them is almost 0.08 mm, with the larger diameter at the end. Tomorrow I'm off to get a 180mm piece of precision ground/hardened 20mm steel rod and then see about finding someone to make the centers for me. Can't do that on the U3. That will/may put an end to any doubts wrt the U3 alignment. In the meanwhile, I'd appreciate any comments the forum could offer with respect to this. Thanks in advance. Best, JHM |
开云体育Hello Julius: What are we looking at in the photos with the indicators? Is the shaft in the head stock ground with a consistent diameter? Or is it a shaft that has been turned as it is clamped? Makes a big difference. Carl. On 4/20/2023 4:28 PM, Julius Henry Marx
wrote:
Hello: |
Hello:
What are we looking at in the photos with the indicators?Let's see if I understand what you are asking and remember exactly what I did. 8^° Started with a piece steel recovered from some kitchen thing that went south, (manual juicer?) which at that time I roughed to ?~20mm. Chucked it, put a center on the far side and cut the 35mm piece on the lathe, faced it and took it down to 19.5mm before turning it around. Chucked it again checking it was properly aligned/centered with the dial, faced it and I then took 20mm of it to ?12mm. Thanks for your input.? Best, JHM |
Hello:
... off to get a 180mm piece of precision ground/hardened 20mm steel rod ...I postponed the 2 hr. journey to the purveyor till I had someone with a proper lathe+skill to make the centers on the rod. for me. Fortunately, I found a chap willing to do the job for a reasonable price and the bar will be ready sometime next week. In the meanwhile and having the week-end to try alternatives, I set up this: It's a 140mm piece of ~19mm rebar dowel found in a skip and cleaned up/roughed to size some time ago. I had no aluminium stock at hand and as the rebar was probably grade 40 at best, I thought it would be easy to work on. I put another center on it, roughed it to size again, made two fine cuts and then measured the diameter at each end. With the readings taken (~ 110mm apart) and the difference calculated, I replaced the shims for the next size I calc-guessed would give me a better result. The last of 8/10 attempts, using a pair of 0.23mm plastic shims gave these results:
Q: if confirmed, is this an acceptable result for a Unimat 3? Can't leave out that all this took much longer than expected because I started using my new set of Taig "high speed steel" bits purchased from a dealer in the US. After much grievance, it dawned on me that I had thrown away US$50. It was a huge disappointment but also a lesson, at least for me. The job was finished in a jiffy using a DCMT21.51 holder/insert purchased last year at Aliexpress. I'd appreciate any comments on the results. Thanks in advance, JHM |
Mr. Pete/Tubalcain (youtube channel mrpete222), "your youtube shop
teacher," has two videos on making test bars for aligning centers. MACHINE SHOP TIPS #95 Making a Test Bar pt 1 MACHINE SHOP TIPS #96 Making a Test Bar pt 2 -- Elliot Nesterman elliot@... www.ajoure.net "The finest jewel cannot disguise a flawed character." |
Hello:
Mr. Pete ...? ... has two videos on making test bars ...Indeed ... I am a huge fan of Mr. Pete and I have seen both videos. 8^) He explains everything very well. That said, most if not all of Mr. Pete's videos are directed at enthusiasts who have or work with a range of tools well outside of what the Unimat 3 is and can do. He has only mentioned the Unimat 3 once, in the context of a "Buying a lathe" video and "... only to show you that lathes come in many different sizes". In the first video you linked to, he shows a bar much like the one I will purchase next week but don't have a granite surface plate to check it. (yet) The U3 cannot pass a 20mm bar and even if I chose to get a 10mm one instead, attempting to make the centers on my 4-jaw would probably not produce an accurate enough result for the test bar to be useful as such. Thanks for your input. Best, JHM |
If you have a decent dial indicator a 10mm bar will be fine. Remember,
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the drilled centers don't have to be perfect as you will be turning the test bar between centers anyway. On 4/23/23 2:00 PM, Julius Henry Marx wrote: Hello: --
Elliot Nesterman elliot@... www.ajoure.net "The finest jewel cannot disguise a flawed character." |
Hello:
... you will be turning the test bar between centers ...I'm sorry if I did not explain myself correctly. I won't be turning a bar. I already did that to see how close I could get to a reasonably good alignment without a proper test bar. Now I will be purchasing an already ground and hardened 20mm steel bar and a machinist with a precision lathe will make the centers for me. The result will be a quality test bar (G6 tolerance and 62HRC surface hardness) for my U3 which will allow me to rapidly align it everytime I need to unmount it for cleaning, maintenance, etc. without the hassle of having to turn a piece of stock. Much like this one ... ... but in a length to fit the U3's 180mm between centers and at a fraction of what the one in the photo goes for. No box needed as a ?1.75" PVC pipe with end caps and a neoprene lining on the inside will do just fine.? Thanks for your input. Best, JHM |
开云体育Hello JHM: We made test bars in trade school. The bars started as 1" hot rolled stock with black bark on it. We turned most of it down to 3/4" diameter leaving an inch at both ends at 7/8". Then we turned both 7/8" spots to the same precise size. All this done between centers. So now you could use an indicator to check the tailstock's alignment, no more test cuts. If you are turning between centers you can cut one end, flip the bar and turn the other end without moving the tool setting and you should be good. Carl. On 4/23/2023 11:44 AM, Julius Henry
Marx wrote:
Hello: |
开云体育Hello JHM: There is yet another option that doesn't use a test bar. Mount an indicator to the headstock spindle and rotate it about the tailstock center. This will tell you if they are in alignment, at this location. You could also extend the indicator so the tailstock is more in its usual location. When
you get your new test bar, be sure to check its accuracy. Both
ends should be the same diameter and spin without any run out.
Carl. On 4/23/2023 3:04 PM, Elliot Nesterman
wrote:
If you have a decent dial indicator a 10mm bar will be fine. Remember, |
Hello, Carl
The advice you gave is spot on. I remember machining a test bar in trade school in the same manner. It is never fail advice! Dick -- http://www.homemadetools.net/ ?SMALL TURRET TOOL POST PLANS? ?LARGE TURRET TOOL POST PLANS ?MINI- ?SMALL QC TOOL POST PLANS? ?QUICK CHANGE LATHE TURRET ?MINI LATHE COMPOUND PIVOT MODIFICATION |