14x40 lathe power feed improvement

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Jun 24, 2010
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I posted this on another forum back in Dec-2017. Now after a few months of happy machining I think its safe to confirm I have the problem licked. In fact, it might be running better than it ever has. Thought some of you might be interested as this style of lathe is quite common among hobby machinists. Aside from the downtime headache factor, at least this has taught me a lot more about my lathe.

The problem started under power feeding spring-2017. Nothing excessive, 0.025-.035” DOC in steel. My clutch started clicking, then complained louder, then finally disengaged altogether with the dramatic clatter. I removed the clutch springs & balls, stretched them a bit, no improvement. By hand I could feel the power feed bar was binding so something was amiss in the apron. I was very fortunate to meet another fellow 3 hours north of me who owns same lathe different name & he helped me through the initial disassembly which was a new experience for me. Thanks John!

After teardown & apron removed I saw the worm gear had worn away at the cast iron C bracket that retains it. Rather disturbing because this machine has seen relatively light duty up until a few years ago. Fortunately the hardened steel worm gear was not damaged. FYI there is an excellent 12-part Keith Fenner YouTube series called Lets Look Under The Old Girls Apron where he rebuilds a distant Taiwan 14x40 cousin of my lathe & he had this same issue. Newer lathes look to have a different layout & improvement. I milled a nice flat in the bracket correcting the wear & John turned me a bronze spacer ring from a Princess Auto bronze bushing that acted as a glorified thrust washer.

After reassembly it was slightly better but clutch still disengaged. Bummer! If I rotated the PF rod by hand it turned ¾ turn free then frictioned up. But this is also where the worm uses up its backlash & starts to engage & pull so the problem could be elsewhere. This began the journey of WTF 10 possible things that might cause friction anywhere in the system.

I removed the carriage top & cleaned up the <cough> ‘scraping’ so it slid better on the ways. I checked all the carriage gears & shafts, they run smooth on the bench. I fiddled with the alignment of the C bracket because it’s a loosey-goosey bolt-on design that can rub on the shaft with the bolt pattern tolerance. I removed the helix gear & its shaft from the apron. Gear was worn but hard to know if sufficiently bad. Every time I made an attempted fix or adjustment I had to re-assemble the lathe to see if it worked.

Finally I had the overdue thought to just check the PF rod runout itself by putting it back in the lathe supported by the clutch cup & tailstock bearing block. Then DTI mapping down the rod length. Sure enough it was bent, max 0.080” at about 1/3 length from headstock. Predominantly in the same plane as the keyway slot. I’ve heard that the shaft can stress relieve itself over time on the keyway, or maybe it got distorted when the bracket wore? Or maybe it was not true to begin with & the wear aggravated it?

My options were straighten or replace, so I pursued both simultaneously. I could find a similar (19mm OD x 5mm keyway) from Chinese lathe which would need to be modified, about $200 & couple months delivery. I wasn’t too concerned about the tailstock end turndown mod. But the thing you come to realize about Asian iron is they do some bizarre things when it comes to drilling roll pins in these rotating parts. Like off center & at ‘hand drill’ angles. So matching that off-geometry to other parts like clutch cup wasn’t too appealing. Enter Modern Tool who went out of their way to source me parts from Taiwan including new helix gear (which engages worm) & some other spares. Unfortunately my shaft was no longer available. New shafts are very expensive. Milling an IMP (7/8”) shaft keyway is do-able, but I was told it would probably warp more than what I had.

So I took my PF rod to a local driveline place where they do that kind of straightening press work. Unfortunately it just wasn’t getting done, so after 4 months of patient waiting I took it back. I then contacted Keith Fenner. He has a lot of talents but shaft straightening is his forte. Plus he is a super nice guy. I shipped it down & he had done within a week within 0.005”. I’ll attach a link where I’m now semi-famous (inside joke). BIG THANKS & LEGITIMATE PLUG TO KEITH!!!!!!

Now with a perfectly straight shaft this baby is finally going together! Not so fast. Again, better but not still not right. WTF. More email exchanges with John. What could be different? I started to get the sense by elimination maybe it always was a bit out of alignment but basically ran despite itself. The driveline will overcome a certain amount of resistance by brute force. I noticed the bracket holes were oversize but shiny on one side (read bowing the bar into submission). There is also no datum, pins or contact registry of apron to carriage, just 2 bolts holding the apron on. That carries the bracket & worm along for the ride. Another potential misalignment?

So I decided to replace the C-bracket & make 2 independent steel blocks, each with longer bronze bushings. This allowed me to float the blocks into position using the rod to dictate concentricity. I made them undersize so that I could shim the blocks to however they fit on apron & match the bolt pattern. The bronze gives me longer sleeve area & also have bushing boss material on either side of worm. This is desirable because when you power feed carriage in either direction or PF cross slide, the worm thrusts to opposite sides & contacts this.

That led me to realize the brass helix gear that engages the worm & drives the carriage also has to be exactly centered to the worm gear. The gear is kind of a saddle profile so if it’s displaced in or out just a bit, the teeth engagement will bind up. So measured it out & made a shim washer to ensure it stayed aligned.

Everyone still awake? :) Now it’s Dec & re-assembly again (I’m getting good at this). New clutch springs, new PT bushing blocks, new brass helix gear, and new alignment. After some careful power traversing & monitoring… It seems happy-happy now. After a couple hours rotating I could still see my rod bluing slowly rubbing off indicating the bushings are sliding nicely & doing their job. The clutch set screws are now set much more conservative than ever which indicates to me the feed power is using its energy traversing vs. overcoming binding & friction.
Clutch related. Note the off center roll pin hole. No, this is not a visual sobriety test. Its actually quite common in these machines. Beware!




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new vs old springs.jpg
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After cleaning up the face of the C bracket, this was my original fix idea - a sacrificial bronze spacer washer just running free. PF rod run-out checking in the lathe supported in clutch cup & tail stock bearing without carriage influence







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Here are some pics of top slide underbelly. Bit of a Hmmm moment actually. If this is what the 'better' Taiwan machines look like, I'd hate to see a rough lathe. The crisp, shiny, induction hardened & ground V rails & flats you see on the topside bed looks over-the-top inconsistent with what actually slides on top of it. Maybe that's the just the way they all are & I was expecting something nicer. I don't think I could use the word 'scraped' with a straight face. The pattern looked way to course for oil frosting.

I blued the surface & carefully blocked off some high points with a fine stone & oil and de-burred the edges. I didn't want to get carried away here so it was 0.0000 type cleanup. I did a before & after pull test with a fishing scale & can say for sure I improved it. But its very subjective. It takes more starting force & drag force with something like WD-40 film on it just as a baseline reference. As soon as you put thicker way oil on, it still requires a bit of 'un-sticking force' but then glides like a curling stone. So that was never a significant hold up issue, but it made me feel better to look in there. I did have chips & sh*t in behind the V wipers. I'm going to come up with a better solution here using a thick felt wiper vs. just the plastic slider (Fenner style).

The underside bed gib clamps (or whatever they are called) are just rough sticks of cast iron. They were ground reasonably flat but again, zero basic chamfering or deburring. I set them up gapped with feeler gauges. There is a fine line between sticking & sliding so required some set screw diddling.







This is showing the final adjustment process of the brass worm gear relative to the mating gear that it drives. I measured gear widths but also turned it while blued to confirm. The brass gear is keyed to a shaft and a washer / bolt to retain it. But I came to realize that simply 'tightening' the end cap could also displace the gear potentially off center. That is bad news. You can only feel this resistance by hand rotating, assuming everything else aligned. I have a feeling mine was always 'out' to some degree but being masked by power feeding. I'm not sure if its just a bad mechanical design or just loosey-goosey tolerances. Anyway, that's why I decided to make a simple bearing plate 'washer' once the gear centering was established & the end bolt gets some blue Loktite to retain the desirable end play position.

Included a pic of the typical shaft lubrication hole. They are often not de-burred or chamferred, so a bit of Dremel grinding made the shaft run smoother. The ID bearing surface itself is not very pretty When you squirt oil into one of the top side nipples, it follows some galleys & down onto various shaft journals in the casting. In my particular case, the holes were plugged up with some waxy mung & probably never saw much lubrication ever. Now when I inject a (light weight way) oil, I can see a indication ring of lubrication.


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I enjoyed reading your thread, it's interesting to see the hidden workings of these Far Eastern machines.
I purchased this Chinese made 13x30 geared head lathe new in 2004, not quite the same as yours and Kieth Fenners machines.
This type of lathe was also produced in Taiwan, but they were a bit too expensive for my pocket, so I bought this Chinese made version
View media item 1463One of the problems I had also concerned the powerfeed, which would leave a pattern of rings on the workpiece when using a fine feed rate.
This was caused by the very sloppy fit of the feedshaft in the bores at the rear of the apron. This allowed the worm gear to move slightly in and out of mesh with the bronze worm wheel as the feedshaft rolled around when rotating in the oversize bores that supported it.
View media item 1462 I counterbored the original holes and fitted needle roller bearings, then made a 19mm O/D steel sleave to pass through the worm gear and sit in the needle bearings. I also had to make a new 15mm diameter feedshaft to pass through the sleave, spent quite a bit of time straightening it after cutting the key way along its length.
Unlike your lathe the support for the worm gear and feed shaft on this lathe is not bolted in place, instead it is cast integral with the apron. It is formed with a trough that holds a small amount of oil, but would benefit from a small cover making to fit between the bronze worm wheel and the leadscrew to prevent swarf dropping into the worm gears from the leadscrew above.
View media item 1461View media item 1460 Just as you have found on your machine, my lathe also has various holes for roll pins and brackets and grub screws which are not accurately positioned and are drilled using hand drills.
I also had to clean up the dreadful factory scraping and chiseling on the guidway bearing surfaces on the underside of the saddle. After checking I found just three pin points of contact on the front bed vee way. It was so bad that I was getting scuffing of the hardened bedway after just several hours of use. After correcting the bearing surfaces on the underside of the saddle I have had no more trouble after many years of use.
After all this I still like some of the Far Eastern machinery, and happily use them along side British machines.
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I counterbored the original holes and fitted needle roller bearings, then made a 19mm O/D steel sleave to pass through the worm gear and sit in the needle bearings. I also had to make a new 15mm diameter feedshaft to pass through the sleave, spent quite a bit of time straightening it after cutting the key way along its length..

Thanks for providing your work. Very interesting. I hope its all running smooth now. I remember being able to source .750" diameter keyed shaft material, which may have been close enough to my stock 19mm. I seem to recall imperial shaft meant imperial key slot & my worm gear was hardened so I didn't have clear line of sight as to how broach it a smidge or make a funky key to adapt them. I also found non-keyed metric shafting but I was told by the time I slotted it (somehow on my little mill??) it probably would banana & I would be back to square-1. I guess thats how I eventually landed on Keth Fenner being the best solution. Glad to here you found a solution. Keep us posted how it runs.
I find this very interesting my friend who purchased a similar lathe calls these things a "kit of parts"
happy hunting
Fantastic work!! I now really hate to say that I have the same problem. I was sourcing the bronze gear, to replace what is left of mine, and this was the first populated site. If I could possibly get your purchasing info for the parts you replaced, I would greatly appreciate it! My lathe is a
Shenwai SW-900GH. I have a mile of play axial play in my PF Rod. This is more than I initially thought I was going to have to get involved with it. Oh well, This is an otherwise fantastic machine. It is surprisingly accurate, and has some power. Ill proly keep this as long as I do my P&W 12X30 Model B. If there is anything else that you can suggest, I am totally open to upgrades for it. Thank you, I would greatly use and appreciate your help with some pointers.

Chuck Howard
Hi Chuck. Thanks for the compliment & sorry to hear about your lathe issue. I have attached the part numbers for my particular lathe which is a model CT1440G, sold by King at the time. I went through Modern Tool here in Calgary (Alberta, Canada) so I cant say that would be a viable option for you depending on where you live, but maybe it will help information wise. I was told the Taiwan factory of this lathe had long since shut down & it was only through some of their existing contacts did they find a 'warehouse' where some parts were stocked. They did me a big favor because I was getting nowhere with other leads. I am also aware that several parts are just not available - the power feed rod in particular. So I made a list of high wear & difficult to replicate items & they did the best they could which was nothing short of awesome as far as I was concerned.

I'm not sure what would be required to replicate the gear. It was certainly more than I could pull off in my shop at the time. If you live in a more industrious part of the world, getting it sourced or made may not be as big an issue. Calgary is kind of the backwater for this kind of stuff. The other thing is this power feed driveline is kind of a domino effect. The bronze gear fits the steel worm gear, the worm is hardened & keyed, it ID fits the OD of the keyed powerfeed shaft. All of these parts are metric. So even if you harvested parts from say a new common Chinese lathe like a Grizzly, there is no guarantee the pitch circles & shaft centers would all line up which ultimately integrate into the apron gear box. I checked a few manuals of other similar 14x40 lathes. they were either completely different or close but slightly different. And unfortunately close doesn't count.

So had I not been able to get outdated stock parts I think having it made would have been the next remaining step. Hopefully your steel worm is fine wear wise because I think the bronze (brass?) is what is supposed to sacrificially wear. Let me know how you get along, I'm interested.


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