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There are several mods to the mini-lathe which are minor, quick to do and help some facet of its operation, reliability or maintenance. These items aren't worth adding a new page for each but they do address details that may be worthwhile, depending on the uses to which the lathe is put.
The picture at the top of this page is interesting because it shows four minor mods in one small area. First, the large hole in line with the spindle was made a bit larger to accommodate the shaft of the handwheel; this allows using the handwheel without removing the cover as I had to do originally. I use the wheel frequently so this saves a bit of fuss installing it; I prefer the wheel to a crank because the grip is always in the same place. The Dremel made short work of enlarging the hole.
The hex bolts which retain the end cover are removed frequently to change gears for threading. To simplify this I made small brass caps for these bolts, knurled them, and pressed them onto the heads(suggested by Engineman). The holes in the cover were drilled out a bit to pass the slightly increased diameter.
Moving further to the right, holes were drilled in the side of the cover which holds the speed controller. In addition, the bottom of this cover has a number of holes added to allow air in with the idea that heat generated by the board would cause circulation from the bottom holes through the top holes. Hard to say if it helps but it doesn't hurt and is easy to do. In addition, the holes in the bottom provide an outlet for small chips which enter via the leadscrew - not foolproof but I haven't had a problem so far.
The last item in this picture is the flat rubber shield on the Fwd/Rev switch. Several owners have developed serious electrical problems from chips entering around the handle of this switch and falling through into its contacts. This little scrap of rubber eliminates the problem -- Radio Shack sells more elegant covers but this works well and cost nil.
Another el cheapo mod is a shield to minimize chips entering the control box through the opening for the lead screw. I drilled a hole in a milk bottle top (I'm looking for a blue replacement) a bit smaller than the leadscrew and added some short radial slits. When the carriage was off for other reasons I simply pushed the shield along the leadscrew. This works especially well for "skimming" cuts ;-)
A way wiper is another quick mod once you find a bit of aluminum angle. A piece of felt is trapped under the angle, held in place with bolts in the holes intended for the traveling steady. My rubber way protector (shown flipped up in this picture) is held by the same bolts. Apply generous amounts of Mobil 1 to the ways and it will be picked up by the felt and automatically redeposited as the carriage is moved back and forth. Use a chip brush to sweep chips off of the felt wipers occasionally. A similar thing could be done on the other side of the carriage but I haven't because relatively few chips make it to that side.
Way protectors help to keep chips off the ways and also off the carriage leadscrew and out of the apron gears - I have never fitted protection for either of these because the way protectors have it covered (so to speak). Way protectors are also easier to make than the protectors most owners fit so this appealed to my lazy nature. The upper protector is anchored by one of the screws used to hold the part that drives the cross slide when making tapers (experience has shown this isn't necessary). A fringe benefit of way protectors is that they simplify chip cleanup. Cutting oil soaks into the soft rubber I used so the protector needed replacing after 2.5 years. The replacement is 1/16" Nitrile from Enco; it seems much less sensitive to oil than the original rubber.
The cross slide on my mini lathe had more backlash than desired, typically 4 thousandths. This would re-appear within a week or so after adjusting the brass nut for 0.001 backlash and would increase slowly thereafter. The brass nut seemed to wear rapidly following adjustment making backlash adjustment an exercise in futility. I smoothed the leadscrew threads with 1500 grit paper and crocus cloth but this didn't solve the problem. The cross slide ball bearing mod only made the backlash more obvious.
Will Hamlyn's split nut mod simplifies backlash adjustment and will, I hope, also minimize wear to the brass nut so backlash will not re-appear so quickly. My notion is that the original adjustment scheme of tipping the nut concentrates the wear areas at the top of the nut on one end and at the bottom of the nut on the other end; Will's mod spreads the wear over the whole circumference and uses all the threads so it should wear much more slowly (it says right here ;-). This mod is larger than most of my mini-mods - it took a bit over 2 hours to complete.
The hole for one of the brass nut retention screws was lengthened by 0.050 -- this was a two step procedure, first the pocket for the bolt head, then the hole for the bolt. I slotted the hole toward the compound but in retrospect it would be better to slot the other hole - the handle of the Allen wrench is trapped between the compound and the screwdriver used to lever the nut apart in my setup.
The holes for the pins were drilled and then the nut was cut with a 0.012 slitting saw; this took two passes, one from each side because of the small blade diameter.
I used finishing nails for the pins. These were 0.070 diameter so I cut the pointed end off, then reduced the diameter a couple of thou with a file (the cross slide was out of commission, of course) for most of the length which was to go into the brass nut. This produced a free fit in the drilled holes; I tapped the pins in place so the large section wedged in the drilled hole and then milled the protruding part of the nails off flush - simple and quick, works well.
I measured the space under the original brass nut prior to removing it. A spacer of aluminum was whittled to shape with drill press and files, including a larger than normal hole in the center and a slot on one side to match the slot in the cross slide.
The split nut is easy to adjust by inserting a small screwdriver in the center hole where the height adjustment for the brass nut was previously. Only the bolt in the slot need be loosened to adjust backlash. The result is backlash of 0.001, about what it was previously immediately following adjustment. I'll update this with info on how long it takes for the backlash to re-appear when I have used it for a while. (After a week of use the backlash is back, similar to before the mod. Perhaps it needs to wear in at first? Readjusted, and the backlash came back. Now, I can't get the backlash below 5 thou -- so, I will try splitting the old nut lengthwise shortly.)
An alternate approach occurred to me as I was doing this mod. The nut could be split lengthwise on the bottom only, then the bottom could be squeezed together (VERY slightly) in a vise. This should close the hole a bit and the springiness should eliminate backlash for a long time by slowly closing as wear occurs - this should work on the minilathe because the leadscrew threads are 60 degree rather than Acme. Engineman mentioned that his Taig uses this scheme and never needs adjustment.
A common mini lathe failure occurs when the carriage slide plate cracks, typically because of over-enthusiastic adjustment (guilty as charged). It seemed like a quick fix so I made a replacement rear slide plate from brass, copying the hole positions with a transfer punch. A cardboard shim 0.023" was about right and things were going along great, taking only about an hour. Since the leadscrew bearing block was off I added an oil hole, a #17 drill nearly through, with a #56 to finish; a bit of felt in the large part of the hole allows oil through and keeps chips out.
On reassembly, the drag from the new slide plate was greater than the old slide plate causing the carriage to swivel slightly when changing directions. I tried to adjust the front slide plate and found it impossible to prevent the swiveling unless the front slide plate was so tight it locked the carriage. The carriage was removed and the "V" in the carriage was examined by inking it and sliding it back and forth on the prism and ways. Contact wasn't good unless considerable downward force was used. I noted that the smooth contact area in the "V" had visible ridges corresponding to the top of the prism; these ridges are easily detected with one's fingernail too. My guess is that the carriage doesn't make good contact with the sides of the prism because of these ridges.
I considered running a 13/16" end mill along the "V", just deep enough to take the two ridges out in one pass -- one of the difficulties with owning a mill is that every problem that comes along looks like it can be fixed with a little milling :-). Instead, I made a tool by end drill/tap a piece of 1/4" rod, then used a 6-32 screw to attach a TPEG 322 carbide insert to the end. This was used as a rake-like scraper to remove the majority of the ridge - it was only about 3 thou - and then a fine file was used to tidy up; cast iron is soft and easy to work by hand for small things like this. The existing contact areas were not touched while removing the ridges. Here are Before and After pictures looking straight down into the central part of the "V".
In addition to removing the ridges in the "V" I replaced my cardboard shim with two 0.013 aluminum shims and also fitted aluminum shims in place of the adjusting screws for the front carriage slide plate. This eliminated the swiveling as well as a slight loosness in the carriage, the original goal. (The rightmost 3" or so of the bed was a couple of thou thicker than the rest so I filed the bottom where the slide plates contact to even things out -- accuracy wasn't critical since the carriage only passes by here while being removed.)
I then checked the "V" in the tailstock where I found and removed similar but smaller ridges. This seems to greatly reduce the ongoing problem I have had with repeatability of the tailstock position, kind of a fringe benefit of fixing the carriage slide plate. Ridges run the length of the "V" at the points shown, corresponding to the top of the prism.
The ridges in the "V" may be from wear (my machine is about 2 years old now) or they may have occurred during manufacture, hard to say. The effects produced by the ridges are small so it is easy to overlook them in use -- I kept running into the tailstock repeatability problem but didn't know what might cause it until I tripped over these ridges. Since it is easy to determine whether the ridges are present by simply looking (and/or feeling with a fingernail) once you know where to look, it would be reasonable for readers to check for this. As noted above, the fix is quick and easy.
I wish I had replaced the carriage slide plate adjusting screws with shims earlier than I did. This was very simple to do and had I done it initially I wouldn't have broken the slide plate and had to make a new one. I had in mind making tapered carriage slide plates to allow adjustment but shims are so easy and work so well that now it doesn't seem worth the effort.
The handwheel on the apron had poor feel due to backlash in the gearing, particularly noticeable when changing directions. I made an eccentric brass bushing, 1/2" diameter with a 1cm hole offset by 20 thou in the 3 jaw with a shim. The apron was drilled and reamed 1/2", one end of the bushing was reduced slightly with a file so it would start into the hole; the bushing was inserted slightly and tried with different orientations to find the maximum engagement of the gears without binding, then the bush was tapped home with a mallet. This minimized the backlash from this source. The apron gears are well made and run true so there is no change in friction vs rotation.
The rack was removed and the mounting holes were drilled out by 15 thou as were the counterbores. The rack was re-fitted and a shim was fitted above the rack at several places to lower the rack slightly, increasing engagement with the apron drive gear. In combination with the eccentric bushing this reduced the backlash by about 2/3. Eventually, I'll probably mill 5 thou or so off the top of the apron on the left side to further increase the gear/rack mesh since this causes the majority of the remaining backlash.
A thin washer was fitted between the handwheel and the apron to minimize endplay, further improving "feel" of the handwheel.
I found my lathe's tailstock offset measurement was much more repeatable after removing the ridges from the "V" so I added a gadget to aid centering the tailstock horizontal position more easily. It is just a 1/4" square bar across the back with 6-32 screws to hold the bar to the tailstock. The center screw is into the base while the other two are into the movable part. My tailstock is fairly close to centered when the top and bottom are aligned. I aligned it as best I could without the bar and ran a file across at the level where I put the bar -- this leveled the thick paint without removing it completely. Then, I put the bar in place.
The idea is that the outer two bar screws are tightened fully. The tailstock locking screws are loosened and the center screw is used to pull the top of the tailstock up against the bar. If it goes too far, the center bar screw is loosened and a shim is inserted, then the screw is re-tightened and the alignment re-checked. If it doesn't go far enough, shims are inserted near the outer bar screws. Once all is well, the regular locking screws are tightened. This approach is simple and seems to work well, at least I quickly got the horizontal error under 1 thou, something which took a lot of fiddling previously. The horizontal setting on my tailstock seemed to drift randomly; my hope is that this mod will also eliminate this drift.
Realize, I never offset my tailstock deliberately -- it has always been so difficult to get it accurately aligned that I avoided moving it except under duress. The taper fixture eliminates the main reason for deliberate offsetting, anyway. If you offset your tailstock deliberately then this mod may be helpful in getting it back to center quickly, although you'll have to loosen or remove the bar to offset.
As time goes on I add more and more shims to my lathe, hard to say where or when it will end. Here, I went to the extreme of adding a place to put the shim rather than shimming an existing part. Simple and cheap, shims allow improving the lathe without making permanent changes which might not go well.
The riser under my lathe wasn't quite enough for comfort so I used a 2x4 between the riser and the rubber feet. This worked OK but wasn't very stable when parting with a hacksaw (sometimes the best option)because the lathe feet are less than 3" apart. In addition, it was always difficult to clean under the lathe because of the minimal clearance. I found a couple of short pieces of 1.5 " square aluminum tube (1/4" wall) at the dump, same as the 2x4's thickness. By adding this between the lathe and the chip tray I got the desired height increase and improved access for cleaning.
To improve stability I added a 10x2.25x0.187 piece of flat steel (another treasure from the metal recycling pile at Newtown's dump) below the chip tray on each end and moved the feet as far apart as this would allow. This was positioned so that the front feet are out of sight under the tray while the back feet are clearly visible in the picture. This improved stability much more than expected, well worth the effort even without the height increase from the other part of the mod.
I purchased M6.1x60 bolts to accommodate the additional 1.5". This wasn't done smoothly - I checked the drawing in the manual to find the size which was given as M5 so I purchased the wrong bolts initially. If you decide to do something similar, look at the machine - not the manual. After the fact I looked at the manual to verify that it was indeed wrong and noticed a couple of other oddities: the manual shows an extension similar to mine below the tray plus there are rubber pads shown between the lathe and the tray -- neither of these were included on my machine from the factory.
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