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Refitting parts after scraping to fit

Earl Sigurd

Aluminum
Joined
Jun 6, 2013
Location
N59 W3 UK
During a brief discussion with Mr King on the scraping course in Germany we discussed the point that, shall we say a lathe saddle was fitted to a reground bed. When the apron was to be refitted it may be distorted when bolted down.

Any experience or comments?
 
Depending on how much has been ground off the ways alterations will need to be made to the position of the feed gear box, long travel rack and the hanger bracket at the tailstock end.
If you've only ground a few thou off the bed you may get away with it but why would you just grind a few thou off the ways ?

Regards Tyrone.
 
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So long as the mating surfaces between the saddle and apron haven't been disturbed, all you have to do is drop the rack and the feed/control/lead screws and the feed selector box the amount that has been loss in the bed/saddle restore. When I redid my SB heavy 10, it was about .020 as I remember. Shim everything down.

Tom
 
I would never correct this by moving a factory located part. I bring the saddle back up to the original center-line as Tyrone teaches. I do check all surfaces to be sure they are flat. Especially around the tapped bolt holes they may have pulled up. Also mount a mag base on the front bottom of the lathe bed when the saddle is setting on the bed with a dial indicator indicating the area where the carriage bolts on and then pushing the saddle to and fro to be sure the saddle is parallel to the bed. You will be testing a factory scraped area that is "original" If you don't do that and just scrape it to fit the saddle will be lower in the front as that is where all the dirt gets in and wears.

As I said if you want to do it the correct way you don't screw up a perfectly good part to align a worn part. As Tyrone said if it is only a few thousands off you can live with it, if not you will need to mill out additional material on the saddle bottom and apply a wears-strip. Rich
PS: On other machines like a Bridgeport I will relocate the saddle and table end brackets as this is simple if it isn't alot. But on a lathe saddle I would never move the rack, quick change, end brackets, etc. Rich
 
I agree that the best solution if you have had the bed re- ground by a substantial amount is to bring the saddle back up to it's original position.

These days it's been made much easier with the advent of the new way material. You can glue anti friction material strips onto the saddle ways. On the other hand you can set up the saddle accurately and then inject plastic way material into the gap you've created.

I prefer the glueing of anti-friction strips myself, especially on smaller lathes. It's whatever you're comfortable with.

Regards Tyrone.
 
Thank you for the replies, gentlemen.

Perhaps my original question was not specific enough though. I was interested in, shall we say the bluing of parts after further sub assemblies are bolted to them.

A specific example would be a lathe saddle is scraped to fit a reground bed. Perfect fit. Then the apron, perhaps a taper turning on the back are bolted on. Has anyone done this and then rechecked the bluing?
 
I might suggest that if bolting appurtenances like the apron onto something like the saddle changes how the saddle interfaces with the ways there's something curiously wrong with the apron.
 
I guess it is possible. I know the apron/saddle interface on my 10EE was not flat when I rebuilt it. So I scraped it flat. It was scraped at the factory as well.

apron interface.jpg

Also I will add if your lathe does not have powered cross feed which not many do unless either very old or very small, after a bed grind you could just machine the apron/saddle interface to bring the apron back up to height.
 
Of course we have Your talking to folks who have done this a couple of times before, no need to re-invent the wheel!! If you do it right and build the assemblies right they will be OK. If you listened during the class you would have recalled as we build things up we have to consider sags or movement due to gravity. We check all the surfaces that are involved in these assemblies for flatness. Some just need to be flat and others need to be flat and have a higher accuracy and PPI.

Doing all this guessing before doing is a waste of time and brain power I have more to do then discuss all this before you do it.
 
Thank you for the replies, gentlemen.

Perhaps my original question was not specific enough though. I was interested in, shall we say the bluing of parts after further sub assemblies are bolted to them.

A specific example would be a lathe saddle is scraped to fit a reground bed. Perfect fit. Then the apron, perhaps a taper turning on the back are bolted on. Has anyone done this and then rechecked the bluing?[/QUOTE

If you've fitted the saddle onto the bed ways correctly you must have also have fitted the saddle keeper strips to the correct running clearance of 0.001" to 0.002".
These keeper strips will maintain the position of the saddle on the ways that you achieved earlier.

If you made a hash of aligning rest of the running gear to the saddle you could encounter other problems. Tight/slack long travel handwheel caused by incorrect mesh of the rack and pinion. Tightness of the saddle at either end of the bed Etc.

Regards Tyrone.
 
I have heard about moving the screw supports on a mill to bring everything back into alignment. That seems straight forward.
Let's say if turcite or moglice didn't exist, how would you go about keeping the gear mesh and screws into alignment on a lathe?

This is something a have spent some time thinking about.
Would it be correct to think: the lathe spindle needs to maintain the same vertical centerline distance to the cross slide screw? There are a lot of gears and surfaces establishing those centerlines.

The Conelly book doesn't really cover this to well. He states scraping straight down is important but doesn't go into great detail about gear mesh.

I am curious to know what the common practice is?
 
Cast Iron or Brass strips fastened on with CSK brass screws " Araldited " in place. Later on Ferrobestos strips came along and you could fasten that on with CSK brass screws also. The practice of moving the feed box, rack and hanger bracket on centre lathes was much more prevalent then. The modern anti friction materials are a real blessing to the re-building game.

I'm not sure I understand the question regarding the lathe spindle centre line/ cross slide lead screw issue. I don't recall that ever being a major problem. If the feed box, rack and hanger bracket have been lowered you can usually adjust the gearing into the correct mesh without too much trouble.


Sometimes the more you think about issues the more you build in complications that aren't actually there. Re-building is a pretty un-complicated game, in theory of course.

Regard Tyrone.
 
This is heresy, but can work.

Industrial modern adhesives work fine as-is, and dont need screws of any type.
E.g. for fitting strips of suitable material.

I use for fitting bearings, and it replaces tight fits, in some cases.
Replaces scraping, in some cases (linear guides need less/no shimming).

E.g. Locktite/Hysol 3478 A&B.
On a 2.2 m (7 foot) linear guide, the adhesive will support == 1.9 million kg load on 2 rails.

3.5 cm rail x 220 = 770 cm2.

125 N/mm2.
= 1250 kgf/cm2.

770x1250 = 962500 kgf. Per rail.
 
My question came up after reading post #123 in the iron tour thread. It got me thinking about all the gear clearances and how they would change after a bed grind.

Cut and paste from the thread- Ruemema does not operate this way and prefers to re-align the carriage by scraping and tweaking the gears mesh after the bed regrind.

I wonder what tweaking the gear mesh entails? Seems like it would be a lot of work and documentation, I can see where wear strips of Moglice would save considerable effort.

http://www.practicalmachinist.com/v...s-pics-301415/index7.html?highlight=iron+tour
 
I can't claim to be an expert on European machines as most of my career I have rebuild American, Japanese and Taiwanese machines, but on a couple of German lathes I scraped the feed screw gear that connects or runs off a gear in the carriage has a cam shaft that can be adjusted to change the clearance. Also on a German built Cylindrical grinder the tail-stock quill was on a cam and could be moved to tweak the taper instead of moving the swivel plate. Both smart designs that never made it into other machine designs. :-) Rich
 
I wonder if they ever tried Bakelite or another plastic type material.

Cotten grade Phenolic, wears exceptionally well in some applications. On a shaper rebuild I'm trying to get back to I got strips of phosphor bronze and brass flat head screws, my first choice was aluminum bronze but I couldn't find it in the right thickness, and then phenolic was 2nd choice but varied too much in thickness. I hope the phosphor bronze wears well.

But so far I haven't actually done it. I'm guessing that whatever it ends up being it will wear well if I increase the oil over what it was getting.
 
These wear strips to get the carriage back up. Are we talking .010 or less? In my mind I see them wrinkling cause they so thin . This me of course .
 








 
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