Where should top slide gib strips go?

[andyf]

I don’t use my top slide in most plain turning/facing operations, and thought it would be an idea to add a locking screw to add a bit of rigidity to my small lathe. Just a threaded hole between the middle two of the four gib adjusters, a little brass slug with one end filed off at 60°, and a screw to push on it, with maybe a little lever to save looking for an Allen key.

While doing this, I began wondering why top slide gibs are put where they are, on the headstock side of the slide when it is set at 90° to the lathe bed, which becomes the front side when the slide is set parallel to the bed.

On the cross slide, the gib is on the tailstock side, because in most operations the pressure is on the headstock side of the dovetail. If the gib was on the headstock side, the pressure would be taken by the gib screws, which would be far less solid an arrangement.

Returning to the top slide, when this is perpendicular to the bed, the pressure will be on the gib screws. When parallel to the bed, it will be on the feedscrew. In intermediate positions, such as 29° for threading, the pressure will be on both gib screws and feedscrew.

To me, the conventional location of the top slide gib seems illogical.  Wouldn’t it be better on the other side of the topslide, or am I missing something?

Andy

[chipenter]

Depends on the maker some are on the out side Myford Drummond and my Faircut are , make adjustment a lot easer my saddle adjustment is on the back and a pain to set and lock .

Jeff

[Fergus OMore]

Actually, there shouldn't be any
The fitting should be so good that they are unecessary but things are not that way for lots of reasons.
I assume that you have these abominations to correct deficiences and cost cutting.Might I now refer you back to Pete Boas excellent notes on your problems with saddle corrections etc?
However, a bit of a lecture - or more?( You CAN delete it all) Pete advised you to change your gibs and alter the adjusting gib screws to bear on the dimples( there may not be even those ) on the gibs.
Now I am telling you to change your top slide gibs from 'bits of rectangular steel' to something which does not rock about like a pea on a drum or FitzHenry- FitzHerbert! GHT saw these problems and recomended that the Myford ones- which were a little better than rectangular strips were pinned, had rounded gib screw ends and had- something to pin the whole lot to fasten down each cut.

If you go to Ian Bradley- on the Myford, you will find that his solution was to add more gib screws!
Tonight, I'm sitting looking at my 'before Myford' vertical slide and I note that it has all these modifications.
Sad to relate, you are not alone. I've got a little Unimat 'clone'- a MJ189 and if I am going to keep it, I am going to replace the 'airgaps' in more than just the top slide.

Am I wrong? Well, my gibs in the cross slide on my Myford have rounded screws but the gibs are adjusted to work in two directions- at 90 degrees to one another- and are in two sections.

Well, now? Lots to do on a snowy weekend, eh?

Regards


Norman

[andyf]

Thank you for your remarks, Norman, but though they relate to gibs, none of them actually addresses my query.

Andy

[Fergus OMore]

The gibs are on the side which face a right handed operative-- using a right handed lathe.
Maybe someone else has other views.

[andyf]

Yes, Norman, that's where they are on every lathe I've seen. But is that just dogma, because that's where they've always been put? Or is there a sound mechanical reason why they are placed where during many operations they, and more particularly the adjusting screws which support the gibs, have to transmit some of the force needed to feed the tool along the work?

It seems to me more logical to emulate the cross slide, and have the gibs on the side where, in the majority of cases, they aren't trasmitting any force.

Maybe someone else knows the reason why they are where they are.

Andy

[Fergus OMore]

I'm hoping that others will contribute but-for what it is worth

I have to repeat my comments about poor quality/low cost/ lousy/ I might be VERY rude/ arrangements.
In an ideal world, a top slide has to be placed in several positions to do its thing. So does it really matter which side it is on? I've got TWO Myford Super 7 topslides which are clamped by two bolts onto the saddle. One of them has a cracked spigot. No, I did not do it- I got it as a gift. I'd planned to do a Jack Radford fixed top slide and the top of the top slide( ) was OK and so was the feed scew and whatever. Radford rarely used the supplied one to do his varied work whilst Tom Walshaw writing as Tubal Cain dispensed with the whole caboodle and designed a single casting called a Gibraltar tool post. Both are still sold by HemingwayKits so they must have acceptance!

So let's move on- into the rest of my Memory zone. Martin Cleeve( Screwcutting in the Lathe fame) had three tool holders. One was a homemade one- with ONE fixing onto a non standard Steel crosslide, the second was the swing tool design- yea, he was at the patent stage with it and a fabricated tool holder on the saddle itself.

So from all this rambling on, the top slide is not exactly all that it is first thought to be. Which side the gib screws are on is of little importance but worse still, is the top slide all that it is cracked up to be?

Let's explain the pun. Cleeve, cracked his top slide as well. That is why Myford made him- a steel one.

I hope that the foregoing is both accurate- and thought provoking. Written without notes or references.

Norm

[andyf]

Thanks for that, Norman, and for reminding me of the names of so many reknowned UK model engineers.

To move on, can anyone else help me with the query in my original post?

Andy.

[Rob.Wilson]

Hi Andy

The reason for having the gib on the side of the top slide that faces you is because the top slide primary use is to add a cut for facing ,were the saddle is locked and the top slide is parallel with the bed ,in that position the force of culling  is on the dovetail and not the gib. Also when using the top slide to turn  a short length the force is also on the dovetail .It is not until as you  say  start angling the top slide   that the loads move from the dovetail to the gib .

Having the gib in that position dose date back to when Henry Maudslay introduced the slide rest to his works ,this is pre leadscrew lathes were all parallel turning was done using the top slide ,were the saddle was move along the bed and locked into position .Holtzapffel also produced his lathes with the same configuration . Same set up on the Lorch lathe.


My Myford,Chrchill CUB and Lorch all have the gib at the front ,but the Boxford has it at the rear . Now I wonder if those lads over in the USA ,Boxford is a Southbend copy took this into consideration  as on smaller lathes it is common practice to angle the top slide to give clearance for the tail stock.


Rob

[andyf]

Thanks for that explanation, Rob. My lathe definitely falls into the "small" category, so the top slide is usually set at an angle so it doesn't foul the tailstock. Just had a look at pics of SBs and Boxfords on lathes.co.uk, and as you say they have the gib at the back.

Going back to Jeff's response, access to the gib screws on the top slide wouldn't really be a problem, because it could be swivelled to give better access to them.

I might move my gib to the back, if the front dovetail (now behind the gib) is well enough finished to act as a sliding surface.

Andy

[DavidA]

I suspect it is mainly to allow easier access to the gib adjuster screws.  Particularly if you have things set up close to the chuck and find you need to take some 'slop' out of the topslide.  This could be difficult if the screws were facing into the chuck.

Both my machines have the screws facing away from the chuck.

Dave.

[Pete.]

My Denford also has the screws on the rear/right of the top-slide. I never thought about why until reading this thread.

[PeterE]

Very interesting to read through this thread, as well as very informative.

I have always thought that the gib strip was placed away from the work point which would result in the X-slide strip to be placed to the right and the top slide strip towards the operator. (The idea being that the work forces would be handled by a "fixed" part of the machine - as said above.) All to make setting and adjustments easy to do and easy to get at.

The only other reason I can find to why having the strip towards the operator would be to make it easier to fit a locking screw for the slide. In that case it would be much more suitable to push against the strip than directly on the dovetail and that screw would then be towards the operator for easy access and use. If fitted away from the operator it would be much more fiddly, perhaps impossible, to get access to the lock screw as the work would be in the way.

BR

/Peter