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| modeldozer:
Hi to all modders, My first try at a bit of a post on here, hope this is the correct place to post, it will take a while to finish. This saga started from brand new. After the cleanup tried to turn some parts from PVC tubing with poor finish and not taking the same cut in and out. Investigation revealed the gib plates on the saddle to be LOOSE :doh: . Trying to adjust this it was soon apparent that the bed ways was not parallel top to bottom, being a lot thicker at the tailstock end. This was corrected manually using various oilstones. The gibs were also adjusted with shims rater than the adjusting bolts. Since then I was able to turn quite a few parts but always had problems with the finish on mild steel and parting off, even plastics. Then added a Soba vertical slide for milling and had reasonable success milling aluminium. Recently I tried to do some simple milling in mild steel with a 8mm end mill with disastrous results, mill broke. Further investigation showed that under force the cross slide lifts up on the right (gib strip) side. Looking into this showed the gib strip to be to small and actually rotating around the adjusting screws. After a failed attempt to fly cut a new one on the lathe, frustration, :bang: nearly putting a sledge hammer to the lathe :hammer:, as a last resort ended up making a new gib strip old school by hand. This was actually quite fast about 7 hours spread over 2 days. Here are some pictures of the process. The final surfaces were lapped with W&D on a piece of thick glass. Before cutting to size the gib was used with some W&D to clean the dovetails. Also noted the saddle has picked up some play, so this was removed and then following methods from here and some other sites on the web the saddle was lapped to the bed ways, testing regularly with mechanics blue. The bed was rechecked wit a micrometer and filed and honed some more for smooth constant fit. As I do not have a milling machine, new gib pates was hand made from calibrated mild steel flat bar, These are thicker and longer than the originals to add more rigidity. They will also be fastened buy SS studs rater than cap screws. (This is not my idea, seen on the web) As the bolt holes in the saddle are all over the place a template was drawn to drill them. Using the modified drillpress as a tapping stand. For the mods/repairs to the bed and saddle the lathe was striped down and a nasty surprise found in the headgear. Looks like a gorilla with an angle grinder made the shift fork :lol: . The detents are also no good, causing the damage to the change gear. This will be looked into later in the rebuild. Hoping to save funds for taper bearings and metal gear. Next up is refitting the rack to the bed, this will be shimmed for better engagement. Unfortunately rain, blocked drains and doctor’s appointments will be delaying this a bit. |
| DaveH:
modeldozer, You are doing a good job :) The more luv and care you put into it, the more your lathe will give you back :) Well done :beer: DaveH |
| loply:
This may be too late, but I went through a similar procedure a few weeks ago and here are some notes for you. Firstly regarding gibs. I fiddled around with mine quite a bit and in the end I replaced all of them - compound, cross slide and saddle - with a new system wherein I tightened the gib down onto a pile of shim stock material. For the cross slide and compound gibs I attached M4 studs into the gib, and the studs subsequently have a nut popped on them and tightened to squish them flat against the shim stock. This works much better than trying to push the gib out and allows repeatable accuracy down to the thinnest shim you've got - in my case 0.01mm. By this means I was able to achieve a cross slide which has absolutely no wobble in it - not even a hundredth of a mill - yet slides back and forward with complete ease. Unfortunately the compound has proved more difficult due to the small surface area, but is acceptable. I also found the gear selector had been wearing on the gears and have since adopted a technique of changing gear ratios then reversing the lever a bit to put the selector in free space, instead of rubbing against a gear. I did also round the edges over quite a bit. Lastly headstock mods - I replaced bearings with tapered roller bearings and changed the pulley ratios to reduce the low gear top speed from 1150rpm to 750rpm for an increase in torque. Between these two mods the lathe changed and I was able to achieve more or less mirror finish on mild steel with no 'lines' showing on the work piece. In conclusion I would highly recommend using shims for your various gibs and if you want a good finish would suggest the motor speed + tapered bearings mods. |
| andyf:
Modeldozer, Despite having no personal experience of Sieg or Real Bull mini-lathes (yours being the latter, I think), I am for some reason :scratch: a moderator of the Yahoo 7x12 minilathe group.There, some say it's better to keep the original headstock gears, to act as a plastic fuse if a tool crash demonstrates that chuck jaws are hard to machine. And others say that metal gears are noisier. I'm not advocating that you stick to plastic, but these are points which you might take into consideration. Andy |
| websterz:
--- Quote from: loply on May 15, 2011, 01:09:12 PM ---This may be too late, but I went through a similar procedure a few weeks ago and here are some notes for you. Firstly regarding gibs. I fiddled around with mine quite a bit and in the end I replaced all of them - compound, cross slide and saddle - with a new system wherein I tightened the gib down onto a pile of shim stock material. For the cross slide and compound gibs I attached M4 studs into the gib, and the studs subsequently have a nut popped on them and tightened to squish them flat against the shim stock. This works much better than trying to push the gib out and allows repeatable accuracy down to the thinnest shim you've got - in my case 0.01mm. By this means I was able to achieve a cross slide which has absolutely no wobble in it - not even a hundredth of a mill - yet slides back and forward with complete ease. Unfortunately the compound has proved more difficult due to the small surface area, but is acceptable. I also found the gear selector had been wearing on the gears and have since adopted a technique of changing gear ratios then reversing the lever a bit to put the selector in free space, instead of rubbing against a gear. I did also round the edges over quite a bit. Lastly headstock mods - I replaced bearings with tapered roller bearings and changed the pulley ratios to reduce the low gear top speed from 1150rpm to 750rpm for an increase in torque. Between these two mods the lathe changed and I was able to achieve more or less mirror finish on mild steel with no 'lines' showing on the work piece. In conclusion I would highly recommend using shims for your various gibs and if you want a good finish would suggest the motor speed + tapered bearings mods. --- End quote --- Can you give us a little more info about the torque improvements you made? I am getting ready to do a top to bottom rebuild of my 7x12 headstock...metal gears, tapered roller bearings, might as well add as much to the job as I can while I'm at it. :proj: |
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