Post By johnoder
Post By pmtool
Post By pmtool
Pratt and Whitney Model C 16 x 30 gets a makeover...
After going back and forth about selling it and getting something a little more recent or refurbishing this lathe I decided that it was worth the trouble, I hope to get it somewhere near its original performance.
The machine is an early 40's war production lathe. I picked it up for cheap knowing that I would be putting money into it.
After a long period of procrastination I am finally working on it.
The spindle bearings were bad, they are a pretty odd ball flanged angular contact set of bearings with a needle bearing in the rear. I was able to locate both angular contact bearings with the help of Eastern Industrial Automation. The bearings are fairly expensive but available. (but so are any precision bearings this size really) I thought about adapting a more modern bearing as mentioned previously on this board but the time that it would take and expense of the other bearings just did not pencil out...
As I speak the spindle is out and I have the new bearings on my desk. I am replacing all other bearings in the headstock while I am as most are standard (relatively cheap) metric radial bearings.
The bed is soft on this guy and had a lot of wear, approximately .015 or so. The lube system to the carriage ways appears to have not worked for quite a while. I decided to get the bed and saddle machined and fitted by a local shop, Thomson machinery, with the machining done on their large Gray planer.
As we speak it is at their shop. They will deal with the saddle and bed and I will deal with the tailstock, cross slide, compound etc. Most of the wear was in the bed ways and saddle so I will at least have a majority of work done when I get it back.
The plans are:
Realign gearbox, leadscrew and shafts, lower rack
New cross slide screw and nut
New leadscrew and reworked halfnuts
new compound nut and maybe screw
rebuild tailstock and fit to new ways
It will be a lot of work but with a basically new spindle and ways this will be a workhorse for years to come.
I will post a couple photos when I get my camera uploaded again....
Last edited by pmtool; 06-22-2012 at 07:11 PM.
Thanks for sharing this. I'm really looking forward to pics and following your progress.
You may want to take a look at the "Wreck Update" and "Another New Toy" stickies in the Monarch forum, especially when it comes to lowering the gearbox. I didn't do that, instead wear strip bearing material got attached to the carriages.
The worst way to fix the issue is to cut the top of the apron, or the mating face for the apron on the bottom of the saddle. This makes it necessary to trim down the gear teeth driving the cross feed screw.
The only right way in my opinion is to do what ever is needed to put apron / saddle assembly exactly where it used to be when new in relation to C/L of lead screw/feed rod/spindle
Thanks Harry, I will look through those post. Here is a photo of the lathe bed on the planer.
John, I did look briefly at removing material between the apron and bottom of the saddle, until I took it apart and realized as you said that it would cause huge problems with the crossfeed screw drive. My plan is to lower the gearbox to match the new center line of the of the shafts and leadscrew. It looks like I will either have to make some offset pins or leave them out all together. I will also have to modify the rack by milling slots where the cap screw holes are to enable lowering it. Sounds like everything will be coming down at least .040. My goal is to not have to do any sort of buildups with turcite or moglice.
Great picture, I would love to see more of the shop where you are having your bed done. Do you plan to scrape the bed after planing?
Although it may appear differently, but I'm one for doing the least amount of work on a reconditioning job as possible. I don't scrape a headstock unless I have to, or relocate gearboxes, etc., I'll use way strip bearing material to build up the saddle. So far I've been lucky, it hasn't been necessary.
How are you going to deal with the apron mounted leadscrew reverse function that is tied into the headstock?
Ronr, I don't have anymore pictures of the shop that planer is in. I think they have been there for 50 plus years and I don't think things have changed too much it all that time. They had someone come in to scrape and flake the bed/ apron after they planed it, so unless something comes up I will not have to deal with that. (which is good because I am not an experienced scraper, although I am lucky enough to work with one who is will to teach/ help)
Harry, the feed reverse and leadscrew reverse linkage will be a tricky one. The connection is between the quick change gear box and the back gear ratio gear box, so nothing directly to the headstock there. However the back gear box will not be moving down, as it is driven directly off the spindle shaft and the headstock has not moved because I had them leave the headstock bearing surface alone. To make up the difference I will most likely make a new part in the linkage between the two gear boxes. Honestly, I am not planning too far ahead until I get the machine back together and have a better idea about what I will be dealing with.
Another intersting one will be the main clutch lever assembly. This is is a shaft that goes right through the bed of the lathe to the back where it links up to the headstock. It will be a puzzle.
I get the bed back from the shop tomorrow. Then it will be painting and putting the spindle together in the next week or two. I finally got some of the more unique bearings in, I was able to get them as new old stock. I will also be rebuilding the bearings in the main drive pulley, they are a back to back pair of angular contacts with spacers so that should be pretty straight forward. I have access to dynamic balancing equipment so I will probably balance the pulley on the headstock as well as the motor while I am at it...
I agree that building up the saddle is appealing. The quotes to plane and scrape in the bed apron were not too much more that a quote I got from another outfit that wanted to plane the bed and build up the apron with turcite. So I figured I would deal with the relocating of components and not deal with having to be extra carful with the turcite in the long run. Plus the older gentleman who is going to help me scrape in the crosslide and compound probably would not touch the thing if it had turcite on it....
Here are some pictures of removing the spindle. The large gear on the front of the shaft is a tight fit, so to avoid too much work with a soft (and large) hammer I grabbed a piece of scrap and drill two holes which just happened to line up with two 1/2 -13 holes in the headstock and also span the back of the shaft. I then used different threaded rods from a typical milling hold down kit to press out the spindle. It worked great. Beware as previously mentioned here on PM (thanks) that besides the obvious locknuts that needed to be loosened, the inner races of the bearings and keyed, and the keyway does not go all the way through. You must remove the key on middle angular contact bearing before the thing is going anywhere! I wish I took a better photo of that to share.
If you look close at photo 2 you can see the needle bearings slightly exposed in the rear end of the headstock casting. I am not sure if I will replace these, they look as though the are in good shape. Anyone know how much radial play the are suppose to have when new???? They are a simple and inner and outer race with loose precision rollers. I imagine one might be able to just replace the rollers with slightly larger ones if needed, though I have not looked into this.
Some pictures of my worn pinion gear, resulting from a lot of time of running with poor spacing with the rack, due to lots of bed wear. I am still looking into how to fix this. I posted a gear specific question in the general section about this but thought I would also put the pics in this thread. Here is the link:
Pratt and whitney rack and pinion gear question
A few steps forward and few steps back.
This weekend I got a bit of time to work so I did a little painting on the lathe bed and headstock. More interestingly I got into full dis-assembly mode. I stripped the apron, quick change gear box and the ratio gear box down to the castings with the goals of:
Finding any parts that need work
Replacing most bearings/evaluating any bushings
cleaning all parts thoroughly (there is years and years of grime everywhere)
The good news is that the vast majority of parts were found in dirty, but otherwise decent condition. The bad news is there are a couple that are going to need work. The major one is part of the single tooth clutch forward reverse assembly. As can be seen in the photo below a major part was completely cracked down the center. Amazingly the clutch still worked fine in this condition as everything was held together. This one is going to be a pain to make...tapers, keyways, etc. It is doable though. Pretty far beyond any welding/ brazing repair! Any recommendations on material and hardness on this piece???
The only other problems were a chipped gear in the quick change box and the worn spur gear of the rack and pinion that I had pictures of earlier.
For those who are interested in such things here are some pictures of the various parts, now waiting to be cleaned:
First is the apron with the cover off
And the apron parts
Quick change gear box parts
Ratio Box parts
And finally a picture of the worn spur gear from the rack and pinion that I am still figuring out what to do with. I found a local gear shop that thinks they can cut it for about 2-3 hours shop rate if I supply a blank. That is if the have the cutter, otherwise they rent it from Ash gear or someplace similar for a 100-200 bucks. Still pondering this one.
Some other somewhat interesting photos (to me anyway and hopefully some others out there)
Looks like this lathes first home was at New Britain in December 42 from that asset tag. Hopefully it will be back to its old self by its 70th year anniversary!
if you have .040 or more of drop, that sounds like doing it all the hardest way possible.
Originally Posted by pmtool
Bring each point affected by the re-grind BACK to original position, be it shimming saddle, headstock, or tailstock - and you have nought else to alter.
If avoiding Turcite or Moglice is a goal, (dunno why..) ..then cast-iron or bronze, made replaceable.
With decent wipers, proper cleanliness and lube, it won't need replacement for many years, and if you put aside a slightly over-thick spare set, Sod's Law sez never...
That should eliminate the need for any changes to apron, shafting or gearing. All of which, BTW, create a bit of a Frankenlathe for the next tune-up. Possibly one you will be doing.
Cool on P&W - looks like the "C" single tooth clutch assembly was redesigned to include cone clutches - sort of like sychronizers in an automotive transmission - the intent seeming to be to slow things down a bit before the immovable teeth crashed together.
But then I could be full of it, too.
If not - what might the cones do?
Spot-on. Attempt to match speeds by dragging the least-resisitive or unloaded component into a velocity match with the more resisitive or loaded one. Most surviving vehicle synchros are more complex - ZF especially so - but same general concept.
Originally Posted by johnoder
Yeah, even broken I thought that was pretty neat. The whole one piece cone (well one piece before it cracked...) provides increasing friction in either direction to get the gear spinning as the single tooth on the gear comes in to be engaged. All regulated by three spring loaded pins in the shaft piece and the v shaped groove on the cone they ride in.
The manual says
"In order to assure correct timing between the headstock spindle and the leadscrew after they have been disengaged for the reversal of the carriage, this clutch is of the single tooth type. A synchronizing device has been incorporated in the mechanism so that the so that the clutch can be engaged without danger of breaking at any combination of spindle speeds and carriage feeds within the requirements of good shop practice."
Maybe someone did not read those last few words!
How much life do you think I would get out of a cone made of 4140 prehard? Looks like the existing one was harder than that...
Bill, you have a good point about the spur gear, while worn, it is uniform, unlike the rack. I was thinking about grinding a cutter to match a unused portion on the rack and recutting the rack on my mill maybe .020 deeper to clean it up. I don't think the rack is too hard. I would then just shim it from the back to make up for what I took off.
About 30 years if he used the lead screw reverse once a day - that is the only time the cones do anything. Besides - you could make a spare!
How much life do you think I would get out of a cone made of 4140 prehard?
I have a similiar lathe- A 1943 Reed Prentice 16"x80" gearhead that was rebuilt/planed in the 70's, may have been the same shop who did the work?
They dropped the saddle/apron and everything else- Turned out to be a real mess. A new rack was cut, a new feed pinion was botched onto the old shaft.
I thought "War machine with perfect ways- Deal of the century!" Knowing what I now know I would rather have a bed with a dip in it. There's so much wrong with it, the deeper I got the more disappointed I was. The time to properly fix the machine would be tenfold it's replacement value. I put it together better than it was, but I'd have done Turcite or Moglice for a proper repair if I could afford the time or if the machine wasn't already F'd when I got it.