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Thread: More New Visby questions
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21st Jul 2019, 12:23 AM #61Senior Member
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Hi BaronJ,
I was relieved to say the least as destroying the shaft was not on my radar. I even contemplated drilling and tapping holes in the bushing and using a slide hammer to try removing it to leave the shaft insitu.. But the heat was definitely worth a try! Yes I have kept them together.
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14th Feb 2020, 11:53 PM #62Senior Member
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Hi everyone..
So it has been a while since I put any time into this project and the headstock is still in pieces.
One thing that I have confirmed is that the intermediate gear shaft is bent. My crude assessment is that the shaft has at least 0.015" runout. The net effect is that the shaft has worn out the bronze bearing at the change gear end.
Attachment 384704Attachment 384703Attachment 38470520200211_205508.jpg
My question is can the shaft be flame straightened or would it be easier to have it re-manufactured? The second part is does anyone know where in Sydney I can get this done? I will need to get new bronze bearings made as well.
Cheers,
Flo
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15th Feb 2020, 07:19 AM #63Philomath in training
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Before applying heat, I would try straightening it in a hydraulic press. 15 thou is not an enormous amount and should come out.
Michael
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15th Feb 2020, 07:04 PM #64Most Valued Member
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What Michael said with the added bit if you haven't done this sort of job with a press before, then take it to someone who has experience straightening shafts etc. With no or little experience, it would be very easy to turn your .015" into a lot bigger number.
Paying someone to straighten it would still be a lot cheaper than paying someone to make a new one.
peter
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15th Feb 2020, 07:22 PM #65Senior Member
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Hi Michael,
Unfortunately I don't have a hydraulic press nor do I have a way of accurately measuring the total runout. The 15 thou was a crude estimation using a couple of vee blocks and an indicator. It's entirely possible that it is more.. The bearing is heavily worn..
Flo
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15th Feb 2020, 07:25 PM #66
Hi Guys,
When I did the refurbishment of my bandsaw, the pivot shaft was bent around 40 thou or so. It only took a couple of minutes with a hydraulic press to straighten it. Its still bent, but its now only around 1/2 to 1 thou at the end.
https://metalworkforums.com/f65/t203...Bandsaw+BaronJ
Post 14.Best Regards:
Baron J.
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15th Feb 2020, 07:30 PM #67Senior Member
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15th Feb 2020, 07:44 PM #68Most Valued Member
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All good. I have a personal experience of trying to straighten a shaft myself once. Got there in the end but but made it worse before I made it better.
Does the shaft have a centre hole in each end? If yes then if you can get access to another lathe somewhere, mount it between centres you will be able to get a real good idea of the run out.
Actually you could possibly get a good idea on you own lathe even though the headstock is in bits. If you still have the saddle/ tool post on it and the tailstock. If you have a bit of round bar with point on it that you can hold with the tool post and a centre in the tailstock. you could hold the shaft between them and using a dial gauge you could get a run out figure. You could even use a drill bit clamped in the toolpost as long as you only turn the shaft backwards in relation to the cutting edge of the drill.
As long as the two centres are close to the same height it would work. You would have to reset the position of the dial gauge for each location you wanted to measure but you should be able to get an accurate reading.
Desperate men etc.
peter
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15th Feb 2020, 07:45 PM #69Senior Member
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15th Feb 2020, 07:53 PM #70Senior Member
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15th Feb 2020, 08:06 PM #71
Hi Flo, Guys,
I held the bar in a collet on the lathe at one end and used a dial gauge to measure it at different points along its length. The bend on the bar was about 3" up from one end.
After straightening putting the bar in the collet from either end showed that the bar was virtually dead straight.Best Regards:
Baron J.
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15th Feb 2020, 08:36 PM #72Most Valued Member
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25 or so years ago I was pressing a new steel timing gear onto Holden red 6 crank. I was using a Hyd press at work during lunch so was rushing a bit. Anyway the spacer I was using to get past the end of the crank onto the gear moved or something and I ended up putting a .025" bend in the crank. Wasn't my finest hour.
Anyway I straightened it on my old Purcell lathe by holding it between centres. Put a lump of 12mm thick X 100mm wide plate across the ways, ( I had something between the ways and the plate but I cant remember what it was. The old lathe had flat ways which was an advantage in this situation) Then I used an engineers screw jack between the plate and the appropriate journal and straitened it that way. I had to push it about .040" the opposite way to allow for spring but after an hour or so go it to about .002". It was easy to spring it more than that just by pushing on it with my hand so I figured being a 7 main crank it would be fine. Which it was.
That engine(although no longer mine) has about 50,000 klm on it now since it was rebuilt and still running fine apparently.
peter
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26th Apr 2020, 11:00 PM #73Senior Member
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Acetal/Delrin for bearings?
So I still need to get the intermediate gear shaft straightened and get new bushings/bearings made.. I'm going to replace the bearings with bronze but I got to thinking about advances in materials since the lathe was built in the 40's. This naturally led me to wonder whether acetal would be an acceptable substitute for bronze in this application? Given sufficient lubrication would acetal be able to cope with the rotational loads and deliver good wear resistance or would it wear too quickly? Would heat build up have any influence?
The current (approximate) bearing dimensions are:
Bearing 1: OD 44mm, ID 38mm, Length 73mm
Bearing 2: OD 44mm, ID 32mm, Length 67mm
I know that acetal is tough stuff but is this sort of application a bridge too far?
Flo
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27th Apr 2020, 08:54 AM #74Most Valued Member
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I cant answer your questions on this but another product to investigate is "Vesconite" https://www.vesconite.com/
I have not used it (and have no connection etc etc) but according to their info its pretty good. That could just be marketing hype as well, however they have been around for quite a while.
regards
Peter
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27th Apr 2020, 09:33 AM #75Senior Member
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Hi Peter,
That stuff looks the ticket.. I'll have to have a look.
Cheers,
Adam
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