My Speedway 7x12 Bench Lathe: Fixes and Upgrades

Note Well!
I am not a professional machinist, nor have I ever been one.  Prior to purchasing this lathe, I had used a metal cutting lathe precisely once in my life, for about two hours; that was in 1980, and the lathe I used then was a monster compared to this small, inexpensive machine tool.  Don't take anything written here as a recommendation -- in a machine shop, I'm not qualified to recommend anything other than following the manufacturer's instructions and seeking competent advice.

Poor Tailstock Release Action

It's been stated that the inner edge of the slotted ways is of uneven thickness, leading to problems with various means of easing tailstock movement and locking unless they involve greatly increasing the travel of the locking plate.  What I found, at least on my lathe, is that the yellow paint that's very crudely daubed about on the inside of the bed casting was also on the lower surface of the ways on both sides of the slot -- where it would interfere with the movement of the tailstock locking plate unless that plate was loosened so much as to encounter the often mentioned problems with rotating and binding.  I scraped the paint off that slide surface, which helped a lot.  If anyone is having trouble with the tailstock not sliding after loosening the nut no more than a half turn, this is worth checking.  To do so, remove the splash guard (to prevent damage), wind the cross slide forward (toward the operator), lay the lathe on its back (carriage handhweel etc. on top) and remove the feet and chip tray to be able to look up inside the casting.  I removed the paint with a machinist's scraper that I had in the shop, a tool used in my lathe construction project, but the paint doesn't adhere very well (the iron wasn't primed, as far as I can tell) and could probably be taken off with any metal tool that can reach into the bed -- a cheap wood chisel, a beat up old screwdriver, a paint scraper, or even a pocket knife might do the job.  The ways aren't hardened, so it's worth some caution to avoid scratching and burring the metal.  After this, my tailstock requires only about 1/3 turn to loosen the clamp enough to move smoothly, though I can now feel that indeed the inner ways are in fact thicker at the tail end than toward the chuck.  Since I intend to convert my tailstock to cam lock when I have the experience and materials, I'm not too worried about this; the beauty of a simple nut for a lock is that if it's too loose, I can turn it some more.

Tailstock Ram Screw Binding

I discovered that binding  in the tailstock ram after cleaning and reassembly was at least partly due to extreme sensitivity of the bearing to alignment -- the bearing on the ram screw is held in position over the insert in the tailstock by two socket head M4 screws.  There seems to be excessive play somewhere in that group, and the first time I reassembled the tailstock ram and handwheel, the wheel was very stiff as I retracted the ram.  Eventually, I found the correct sequence of reassembly: install ram, install anti-rotation screw (turn grub screw to contact, back off at least 1/2 turn, and lock with jam nut), then insert tailstock lead screw, screw into ram to hold in place before installing retaining ring.  The ram should now be moveable by turning the bare, unlubricated end of the handle with fingers.  If so, all will be well after reinstalling the handwheel.  In my case, the tailstock ram is now completely smooth except for a trace of binding (it feels as if the screw isn't completely straight) in the last half inch of in travel.  Since this part of the travel is only used to eject Morse Taper accessories in any case, I'm not too worried about it.

Difficulty Removing Saddle From Bed

When I removed the saddle from the bed for cleaning, I found considerable binding just as the saddle came even with the end of the bed -- no overhang yet, just on the very last bit of the ways.  What I discovered is that the lathe serial number, which is on the top surface of the ways, at the back on the tail end, is stamped.  The stamping process raises the metal displaced by the stamp into a bump around the stamp impression.  If this happens on the ways of a lathe, it will interfere with the travel of components that have their gibs or guides adjusted for the unaffected part of the ways.  I solved this by using a flat file to remove as much of the raised metal around the serial number as possible without cutting into the (unhardened) ways anywhere else.  In the event, I put a few minor scrapes and nicks in the area around the number, but none of them have raised metal and none are in the area normally traversed by the saddle.  The tailstock, of course, uses only the inner edge of the ways, and the number was stamped at the outer edge -- so, points to Sieg for putting the serial number where it won't interfere with normal operation, but only partial points; that number could just as readily have been stamped on the lower portion of the bed casting (say, the top surface of the foot lug), where later application of paint wouldn't have made it unreadable, but it wouldn't intefere with removing the carriage when needed.  Update: I've since found, in connection with the tailstock movement, that the ways are a small amount thicker (something like .005" to .010") at the tail end, compared to a point a few inches left of there; this most likely contributes to the binding of the carriage at the extreme end of the ways.  Again, this isn't a big deal in normal use, because the carriage can't travel that far even with the tailstock off and threading dial removed; it's only of concern when removing the carriage for cleaning, maintenance, upgrade, or repair.

Cross Slide travel limited by splash guard

I had occasion to use the full travel of the cross slide, when facing a part that extended slightly beyond the diameter of the stock 3-jaw chuck.  I wanted to keep the compound at 90° so I could use it for infeed while the carriage was locked on the (disengaged) lead screw, and I needed a particular tool angle to get a good finish with a "drag" facing cut, out from center.  I found, however, that I couldn't get the tool to center because the back end of the cross slide hit the splash guard.  Well, I have a long term plan to make a taper attachment, and the spalsh guard would have to go before I could mount something like that behind the lathe, anyway, so unscrew four screws, and the splash guard is off.  Part faced, all is well.  Added bonus, I can now (if needed) remove the cross slide from the carriage without having to take the tailstock off, dismount the right lead screw bearing, and run the carriage off the rack to the right -- that makes me much more likely to take the slides apart and clean the grease out of them, now that I'm sure they're better off with only oil.

Gear spacer stuck on left end of lead screw

When I first tried to change the gearing from the factory setup fine feed (256 spindle revolutions per inch feed, A:20, B:80, C:20, D:80 in the lathe's gear chart convention, or 16:1 reduction on a 16 tpi feed screw), I found that the spacer sleeve that keeps the final 80T gear at the proper position to mesh with the outer gear of the compounded pair didn't want to come off the screw, though the gear itself came off with a carefully balanced pull.  With some effort, I was eventually able to pry the sleeve off the shaft, cleaned up the burs created by removing it with a file, and filed away the burrs I could feel on the edges of the keyway.  The gear setup I needed had the sleeve on the outside, instead of the inside, and it went on snugly but not with undue force.  When I went to remove it, however, I found it stubborn again (though less so than previously).  After closer examination and some careful tests, I found that the keyway in the lead screw is of non-uniform depth; deeper at the shaft end, where it might reasonably have been measured in an inspection (giving Sieg the most credit for trying to build these little lathes well -- they have been responsive to end user input over the past ten years in terms of adding features and capacity), but shallower close to the pillow block; the gears would slide on with a little push and come off without too much pull, but the metal sleeve would jam in place.  After carefully cleaning up the sleeve (which had burrs inside both ends of the bore, with the black oxide coating covering both burrs indicating it was never properly deburred in manufacture) with a half-round needle file, I used a tiny square needle file (needle file set and handle left over from model airplane building) to file the keyway slot deeper in the sleeve, until it would slide freely to the farthest point on the screw shaft that would be needed.  No further problems in changing the gears on the lead screw.  Some gears are rather tight on the B/C bobbin sleeve, but given that the gears are plastic, I expect that to be a self-correcting problem over time.

Through bore in three jaw chuck too small

The spindle bore in the Seig mini-lathes is about 13/16", just about the biggest it can be without reducing the contact length of the #3 Morse Taper socket at the chuck end of the spindle.  Unfortunately, the 80 mm three jaw chuck that comes with the lathe has a through bore of just about 5/8" -- which is much too small to pass 3/4" drill rod.  Since I've been working with 3/4" drill rod quite a bit lately, I've been noticing this shortcoming quite a bit, though I should emphasize that this isn't so much a defect of the lathe as a consequence of choosing the 80 mm chuck as the standard one.  A larger chuck would naturally have increased the price of the lathe (especially given that the chuck supplied is of surprisingly good quality for the price of the machine), but would have had a larger bore.

Fortunately, careful examination and disassembly of the chuck revealed that nothing structural would be compromised by boring the center hole in the chuck to a larger size, though if I went more than a whisker over 3/4" I would wind up cutting into the heads of the three screws that secure the scroll retainer inside the back of the chuck.

I removed the jaws, scroll, pinions, and the retaining pins for the pinions before starting this operation, but had to have the scroll retainer and its screws in place so that the resulting bore would be the same diameter all the way through.  Using my newly completed boring bar holder and the nice new set of boring bars I purchased a week or so ago, I started boring.  One of the first things I noticed was that the metal of the chuck didn't produce long, curved chips like the aluminum and steel I've machined up until now; instead, the swarf comes off as fine particles, not much larger than beach sand.  Once I saw how black my hands got, I decided that must mean the chuck body, at least, was cast iron (which makes perfect sense; it's much cheaper than steel in that size chunk, machines well but can have required machining reduced by casting in most of the final shape, and is plenty strong).  I took it slow and easy, never trying to take a cut of more than .020, using the power fine feed (about .004" per revolution), then stopping the spindle, reversing the feed, and power feeding back out without changing the cut depth before adding more in feed.  Periodically, I'd gage the hole with a piece of unmachined 3/4" drill rod.  When I got to the stage where the rod would pass the near end of the hole, but would interfere partway through, I started making repeated passes inward and outward without changing the feed setting; after about eight passes, the tool had mostly quit cutting, and the 3/4" round bar passed easily through the chuck.  Now, when I want to end face and center drill a piece of hacksaw cut 3/4" rod, I can keep the end I'm working on short and stiff, and keep the center in the center.

#2 Morse Taper arbor too long -- ejects at 5/8" tailstock ram travel

This isn't a problem with the lathe proper -- I purchased the tailstock drill chuck and its attached MT2-JT33 arbor from Harbor Freight, separately from the lathe (because Homier doesn't sell any of the accessories; otherwise, I'd have gotten the drilling chuck and a couple other things with the lathe), but it's related to the design of the lathe, in that the tailstock ram doesn't have enough internal clearance to accept full length #2 Morse Taper shanks, even without a tang end.  Several people have recommended simply cutting off the tang and/or a half inch or so of the taper on the full length taper arbors in order to gain that half inch of clearance for drilling -- more critical on the 7x10 (which is really a 7x8 using between centers measurement) than on the 7x12 or the Micro Mark 7x14 -- but I wanted to keep the full length of the taper; my thinking was that shortening the taper would reduce the contact area between the arbor and the socket, and might increase the likelihood of damage such as fretting or spinning .

My solution to this dilemma was to mount the entire chuck and arbor assembly into the three jaw chuck on the spindle, with the lathe chuck jaws gripping the hard, fixed section of the drill chuck that has the round holes for the center pin of the chuck key (the chuck body itself).  By advancing a dead center into the center drill mark in the end of the MT2, I was able to push the drill chuck against the lathe chuck's center hole and have everything self align as I closed the lathe chuck's jaws, and the drill chuck body (even on this very inexpensive chuck) was hard enough that the lathe chuck's jaws left no mark.  With the chuck and arbor assembly mounted in the lathe chuck, I then removed the tailstock (to get clearance for the carriage) and mounted a 3/8" twist drill in my newly made boring bar holder which, having been drilled in place on the lathe, is precisely at center height.  Careful adjustment of the cross slide allowed me to feed the twist drill into the center drill in the end of the MT2 with the carriage handwheel and drill a hole about 3/4" deep.  I thought I was done at that point, but a test in the tailstock revealed that the ram screw, though it would enter the hole, was engraving very shallow threads; I needed to enlarge the hole a bit.

After remounting (and recentering) the chuck and arbor in the lathe chuck, I put my smallest, shortes boring bar in the holder and used it to bore the hole in the MT2 another .030" larger (total I.D. theoretically now at .405"), which handily clears the ram screw in the tailstock.  The arbor now ejects at about 3/32" from the zero mark on the tailstock ram, which I find much more acceptable -- enough so that I haven't bothered to drill and bore the hole the extra little bit that would be required to get to the zero mark, and won't unless I find I need that fraction of an inch clearance to end drill a part at some point.  Best of all, the hole still fits inside the reduced diameter nub at the end of the MT2 taper, so the exterior form of the taper arbor is unaffected.

Carriage handwheel gears collect chips and jam

Nearly every web page with extensive information about the Sieg made mini-lathes mentions putting a cover of some sort over the open handwheel reduction gears in side the apron.  As provided from the factory, these gears are completely exposed on the lead screw side of the apron, and the grease that's recommended to smooth operation and prevent wear catches chips and holds them in place where they'll pass through the mesh of the gears again and again -- chips that can be large enough to completely stop the carriage motion, possibly causing the machine to stall during a cut, or leading to variations in feed rate that in turn cause variations in cut depth as the tool cuts through the deflection in the work where the feed slows.

I finally found the situation annoying enough to prompt me to disassemble the carriage and fix the problem.  Of course, I had to dismount the tailstock, remove the right end pillow block supporting the long feed screw, and then run the carriage off the rack to the right, followed by loosening the rear gib enough to pass the thicker section of the back way and sliding the carriage off the ways.  After removing the apron, I reinstalled the saddle and slides, knowing I'd probably need to use the lathe while the apron was off.

Complete disassembly of the apron, thorough cleaning to remove the lithium grease I'd put there when I originally cleaned and set up the lathe, and disassembly of the split nut mechanism, left me with a bare casting and the pressed in axle for the rack gear.  I set the split nut sections back in place and used them to mark the necessary clearance so the installed guard wouldn't interfere with their movement; this mark was extended across the full height of the apron and across the top and bottom surfaces to provide a referense.   Then, using a sheet of .032" brass (I'd have used .025" or even .015" if available, but this was the only thickness the hobby shop had when I stopped in), I laid the apron casting on the brass in position so that the factory cut edges of the stock would form two edges of the finished guard, and scribed around the edge of the apron to mark the shape onto the brass.  Ten minutes with a pair of aviation snips and fifteen with a file, and I had a neatly cut and perfectly matched brass plate that would completely cover the gear well milled into the apron casting -- except that it didn't have a hole for the rack gear.  Okay, I'll come back to that.

A little careful dry fitting confirmed what I'd read on at least one web page about this fix; I'd need to reduce the thickness of the gears by a fat smidgen to avoid having them rub, hard, on the cover plate.  In fact, the best I could measure suggested the gears were about .010" proud of the flat surface of the apron -- so I needed to take about .015" off them to provide a running clearance.  The handwheel gear was pretty easy; it had a flat face on the exposed side, and a raised bearing area around the shaft that passes through the apron to accept the handwheel.  After pushing the saddle into position and tightening the back gibs (which I had to adjust anyway after removing the carriage, because in working adjustment it's too tight to pass the tail end of the ways) and chucking the gear by the shaft (which, I'm gratified to report, was hard enough that the jaws didn't mark it at all), I faced off .015" and was done.  The carriage gear was a little more challenging; here, I couldn't easily face from the plate side of the gear because that was the side with the shaft, but the opposite side has the raised bearing surface that rides on the cast iron of the apron around the pressed in axle.  Okay, well, it's not that difficult.  I chucked this part by the shaft as well (with the gear protruding into the newly enlarged opening in the chuck -- it wouldn't have fit before I enlarged the chuck bore, as the gear is 17 mm across and the old hole was only 16 mm diameter) and started by facing .015" off the relieved portion, leaving the bearing surface proud by a total of .045" or so, then faced the same amount off the bearing surface to reestablish the same clearance, but with the entire assembly shortened by that critical amount.

That done, I measured carefully, marked the location of the center of the carriage gear's axle, and drilled through the brass with a 1/2" twist drill -- in this case, since I was going to have to enlarge the hole and fine tune it's location anyway, I didn't both to step drill.  I then used a nibbler to enlarge the hole, followed by a round file to bring it back to round and fine adjust the position until the plate would mount over the gear shaft and take the right position.  Five carefully placed punch markes, and I was ready to drill the screw holes in the plate.  Those holes were used to locate the punch marks in the apron, though the thinness of the brass meant I couldn't use a transfer punch; as a result, the holes weren't perfectly aligned.  No matter; they weren't far enough off to cause trouble drilling, and in a short time all five holes were center drilled and drilled to the tap drill size (I think it's #44, but the drill that came in the tap and drill set isn't actually marked, that I can see), 1/2" deep, and a little later they were cleanly tapped as deeply as the 4-40 plug tap would cut.  I had to adjust the positions of three of the holes in the brass in order to get the screws to fit in all the holes, the work of a few minutes with a round needle file, and then it was time to start putting things back together.

I adjusted the split nut gib much more snugly than the factory setting; now the split nut has almost no play (or "shake") when engaged; the bottom, adjustable piece has nothing discernible, while I wasn't able to tighten the top section enough to remove the last .005" or so -- but if one jaw is solid, there shouldn't be any end play when the split nut is engaged.  In combination with the tension adjustment on the handle detent (a spring loaded ball bearing that holds the handle in the disengaged position) I was able to set things up so that the handle moves readily, but won't vibrate into engagement (which could cause a disaster during a chattery cut).  Careful alignment of the apron with the lead screw was easy before tightening the apron mounting bolts in their slotted openings, and now everything moves smoothly -- and despite making about half a pound of chips since installing the guard, there's no evidence of binding or hesitation in the long feed either when hand feeding or under power.

Broken 80T change gear

I'm embarassed to admit how I broke this, but it is something I've had to fix on the lathe, and is related to a deficiency in the design.

First, in order to do accurate facing, one must lock the carriage in place; otherwise, the cutting force may move the carriage and result in the tool backing off from the cut, producing a sharply conical face (and losing any zero setting that might have been made).  The 7x12 lathe, however, comes with no means of locking the carriage other than to overtighten the screws on the carriage retainers; these plates have been known to break after prolonged use of the lathe, because the three screws that tighten them flex the plate against two locked screws, similar to those on the cross slide and compound slide gibs, that set the clearance of the plates against the underside of the ways.  If one doesn't wish to lock the carriage with the guides (which is also annoying to do, since they have to be tightened with a 5 mm hex key from underneath, and only the back side locks are accessible), one can put the tumble reverse in neutral and close the split nut on the feed screw; the angles are such that even if the screw were as frictionless as high quality ball bearings, it wouldn't turn under pressure from the carriage.

Unfortunately, with a stock machine, the carriage travel toward the headstock is limited by the long. feed hand wheel bumping into the motor controller housing; if that controller is relocated (as some users have done), the next limit is when the back of the saddle hits the motor cover or the inside of the splash guard.  If one is working close to the headstock, was just using power feed to make a cylindrical cut, and then (with the lathe power off, of course) closes the split nut to lock the carriage, one might not notice (while trying to cut right up to the spindle flange, say) on powering up the lathe motor that the lead screw is slowly revolving.

The creaking, cracking sounds from the change gear housing serve as an immediate reminder; I stopped the lathe with the panic button, but it was already too late; the split nut was locked closed by the force of the lead screw, and the hand wheel was so hard against the motor controller housing that I couldn't even take the pressure off the split nut.  I tried reversing the lathe motor, but nothing happened -- that was when I knew I'd broken something.  Okay, obviously I'm going to have to take things apart to get the carriage free anyway; off with the gear cover, and once again reverse the motor; no good; the final 80T gear turns, but it doesn't turn the shaft.  Looking closer, I can see plastic shavings extruded by the Woodruff key.  This is Not Good.

Well, it wasn't that bad; I had no significant problems disassembling the gear train, and though the 80T gear might have been salvageable, I don't have a chuck large enough to chuck the gear in order to bore and sleeve the center hole (a 4" four jaw would do it easily, but the 80 mm three jaw that comes with the lathe is about 5 mm short with the outside jaws).  At this time, I also didn't yet have a faceplate, and in any case I'm not sure how I'd go about indicating in a gear without any smooth circular surfaces I can measure for runout.  Fortunately, a replacement gear is only about $5 from, and with online ordering and even economy shipping, I had the gear in hand before I had time to miss it properly; the one setup where I needed slow feed, I used an 65T in that position and lived with a coarser feed without undue hardship.

From one way of looking at it, in fact, this was a good thing -- a plastic gear that's cheap to replace (a full set of these gears is only about $30) is a far better thing to break than twisting or bending a lead screw, cracking a split nut, or springing the change gear banjo.

Adding a 21T change gear for better metric threads

Honestly, I haven't tried to cut a metric thread yet.  Certainly there are a bunch of gear combinations that will do reasonably acceptable jobs of appoximating metric threads -- typically with less than half a percent error, which is plenty close for a thread that will engage for six to ten turns, as in a nut.  However, a specific metric conversion gear is better than hoping you can come up with a bizarre combination of gears that will give the change you want and still fit on the banjo.  The perfect metric conversion gear is 127T -- with the inch legally defined as 25.4 mm, this gives an exact conversion (though if you have an inch based lead screw, you'll still have to keep the split nut engaged and reverse the lathe for each cutting pass).  Unfortunately, a 127T gear won't fit on the 7x12; it'd be huge, and there isn't room inside the cover or between axles on the banjo.  Next best are 63T and 21T, both with very small errors in common metric pitches. sells a gear that can be made into a 21T change gear; as sold, it's 12 mm thick, with a similarly thick 14T gear molded on as a compound set.

Following the instructions provides on the page where they list the gear, I faced off the 14T adjunct and reduced the thickness of the 21T gear to 8 mm, aka 5/16".  I then drilled out the center to 1/2", and bored the resulting hole to 15 mm (actually, I left it about .005" undersize).  The plastic of the gear machines like very soft metal; it forms a curly chip that sticks to stuff from static charge, and chatters if you don't maintain enough feed; cutting speed seems to like about 50 sfm, give or take.  In the facing process, I managed to push the gear out of the chuck twice before I had the combination of cutting speed and feed rate figured out, scarring up the teeth; I trimmed off the burrs with a sharp knife, and the gear seems to mesh okay (though I haven't, as of this writing, tried a cut with it).

After machining the hole, turned a piece of 3/4" hot rolled round to 15 mm O.D., then drilled and bored to 12 mm I.D.  I parted the piece off with a hacksaw (don't have a parting tool yet),  squared up the ends and faced to a little thicker than the gear.  Check the fit: a little snug; rechucked the gear and took the finest cut I could manage off the inside, and repeated until the bush was a light press fit (being careful to deburr everything before each fit attempt).  Two minutes with the hack saw yielded a slot in the bushing; five minutes with a needle file widened it until the bushing would slide nicely over the sleeve that holds the B/C gears on the banjo, without binding on the key.  Press the bushing into the gear -- now it won't go on; the slot closed up a little.  Okay, take a little more off the inside of the gear, until the bushed gear is a snug slip fit on the keyed sleeve.  Finally, press the bushing out of the gear (had to use the back of my MT2 drill arbor, pushed with the carriage, as an improvised press -- wouldn't think of it if real force were required, but this only took a couple pounds; I just couldn't get my fingers in the hole), an chuck it with the sleeve inside to trim the bushing to the same width as the gear before pressing it back into its final home.

I think the bushing is looser than it ought to be -- if I hold the sleeve with the gear on it, I can slip the gear on the bushing with my fingers, but that may be more force than the gear would experience, especially as this one would normally be on the stud, where the torque is lowest.  I'll update here when I have a chance to try something like a 1.5 mm or 2.0 mm threading cut.

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