Top slide std positioning

All my lathes over the years, big Colchesters to current Boxford VSL have had the top slide (compound to 'Mercans) in the std British and European position of parallel to the bed. Only moved for screwcutting to the usual 29 and 27.5 degees etc.

I notice in all the American books, manuals, and videos i watch, virtually every lathe owner/operator has the topslide set permanently for screwcutting.

I also see that many use a Travadial or DTI for carriage movement for facing etc, as the topslide is not parallel to the bedways.

Is this just how they are taught, are there advantages for the topslide not being parallel to the ways? I personally think that cutting forces, are probably better in this position, especially parting off, as the forces are going (nearly) through the leadscrew rather than against it and the dovetail sides.

Just been thinking of adding a second locating hole for the Bison QCTP with the topslide set over.

Your thoughts?

I normally keep the compound at the correct angle for screwcutting. For almost everything else I feed with either the carriage or the cross slide. Occasionally I set the compound to the correct angle for cutting a taper or for re-centering a shaft. If I kept the compound set parallel with the bed there would be interference with the tailstock.

I almost always use the carriage rather than the top slide. I know the carriage is parallel with the work whereas the topslide may not be spot on.

As John mentioned it also helps keep the topslide out of the way of the tailstock.

As John and David I use the carriage or cross slide for most of the turning operations. I set the top slide to about 6 deg. from the lathe centre line so when I advance the top slide get a very fine feed when reducing the diameter of the work. I use between 29 and 30 deg. when screwcutting.

Thor

Indeed. 5 odd degrees, and a 1 thou mark on the dial = a tenth of a thou cut. Old turner's trick.

My top slide is used only for facing work. For normal work it is set parallel to the bed and is spot on. Also the Bison (Dickson copy) is always square as the location peg is accurately located in a hole in the top slide.

The top slide only gets moved for screw cutting or short tapers (up to MT2). It is also never in the way of the tailstock.

Thanx for the initial replies, 3 so far in favour of a set over topslide...

Perhaps someone will chime in re cutting forces re positioning. We all know a solid block in place of a top slide gives more rigidity.

Another reason to leave the compound set up for thread cutting is on some lathes the compound handle can foul the tailstock base when turning between centres. Some people take the whole lot off and use a Gibraltar type toolpost for more rigidity which if fine if you don't use the compound very often !

The 5 deg fine cut trick works very well - as long as you are using a nice sharp cutting tool !

4:0 Blimey.

I never set the topslide over for screwcutting. Far less bother to move it over a few thou for each cut and it works for any thread profile.

It doesn't need to be set more accurately than within a degree or so for facing/depthing (do the trig) and my main use of it is putting the tool tip in a convenient position when working with tailstock support and turning tapers.

The occasions I need it set very accurately parallel are few - just for when using it to put on an exact length cut that has to be parallel such as a register, but I'm more likely to cut the register slightly short using the saddle then use the topslide to face it to length.

I';m a fan of 'gibraltars' as well - I made one for my mini lathe.

Neil

I'll generally set the compound at half-angle for screwcutting 10 TPI (2,5mm P) and coarser in steel, but wouldn't bother for brass or LG2.

But by default I leave it parallel in case the job needs a precise face-off - the 0,25 mm divisions on the Warco's carriage dial are a bit coarse for trying to judge to a thou.

I think your default should depend on the sort of work you do and the particular design of your machine - ain't no hard and fast rule in my book.

I leave my top slide parallel to the bed, as indicated by the built-in protractor. Like Neil says that is more than adequate when facing to length. I always screwcut with the top slide parallel. The top slide only gets moved for longer tapers. For tapers over 3" or so I set up the hydraulic copy unit with a pattern. For non-critical chamfers I just swivel the toolpost.

Andrew

Always left at screwcutting angle, but as I have a modified GHT topslide, the topslide leadscrew handle is well out of the way of the tailsock. Full DRO, so cut is set by readout and not scales.

Most of the time I don't even bother to fit the top-slide but use a cross-slide mounted toolpost. Only time I would use the top-slide is for short tapers. Even screw-cutting is quite easy without the half angle set over, just feed the tool straight in taking slightly smaller cuts for each pass.

The carriage handwheel has a dial and I find this to be quite accurate provided I account for considerable backlash in the rack but usually turning up to a shoulder it is quite sufficient. The cross-slide toolpost is definitely more ridgid than the top-slide mounted toolpost.

John

I've never thought about it before. Just had to go into the, still cold, w/shop to check, it's set about 45 deg. so clears tailstock etc. Only changed for small taper turning. Am making a solid block to replace the topslide, just so much to do.

Mine sits at a moderately random angle close to 25° which does for all screwcutting using the zero-to-zero / zero-2-zero method and keeps the handles nicely clear of everything. Also puts a significant fraction of the cutting loads in both axes directly onto solid slides rather than via the screw.

Way I see it parallel to the bed puts all the feed in cutting loads direct to solid metal but now the longitudinal loads go via the screw. Also gets in the way of the tailstock. Ability to do short parallel turning to measured lengths is something of a misnomer. Needs to be set dead nuts parallel to the bed for accurate results, significantly sub thou error at at least over whole travel is desirable if the results are to be trusted. A right pain to achieve with the usual adjustment facilities, especially on smaller more economically priced machines. You could dowel it I suppose. Small lathe topsides aren't really up to snuff for this sort of thing anyway. The monster on my Smart & Brown 1024 10" swing machine is but that has an accurate saddle travel dial so its all bit irrelevant.

In the time it takes to get the saddle dialled in twice you could have a micrometer bed stop made which is far better for travel setting. Ooodles of dirt cheap micrometers on t'Bay to break up for the barrel. Add a cheap set of gauge blocks in" won't wring together" condition from same place to extend the range and you're done. You only really need the bigger ones but a gash set can be handy for all sorts of set-up checks. If you want to be real fancy make a clamp to hold a stack of blocks together.

Set 90° to bed and all the cutting feed in loads go through two sets of screws. Not ideal especially on small machines where the screws are inevitably a bit wimpy. Not helped by wear.

Set at exact screw-cutting infeed angle. How exact is exact? Same mechanical issues with setting dead right as with the parallel to bed arrangement and even harder to measure WTHIGO.

In a practical world adopting the zero-to-zero screwcutting method resolves pretty much all issues. According to Geo. H Thomas that was the way his star turner did things. No way am I gonna argue. Especially as its the only method that makes it easy to figure out whats gone wrong when its thread doesn't fit!

Slightly OT but closely allied. I presume everyone knows that the easy way to align a 4 way or QC body with the relevant sides perpendicular and parallel to the bed is to extend the tailstock barrel and lightly press the body up against it. I use one of the MT taper holders acquired for my Dickson T2 s over the years when purchasing several tool holders as an (almost) affordable set. Knew they had to be good for something!

Clive

Lots of talk about how various angles are optimal but like most things there isn't one answer. If you don't have the topslide parallel to the bed, how would you make a precise axial cut? Using the carriage handwheel? Even with a DRO, applying the required movement would be tricky to say the least

Nowadays I usually remove the topslide which is only used for short tapers (eg 40 taper recently) and mount the toolpost directly on the cross slide. To answer my own question, to make precise axial cuts, I use the tailstock (which has a simple digital scale) to push the carriage the required distance. The rest of the time, a topslide has little purpose and contributes to slop and loss of rigidity.

Murray

I use the top slide lock, and tighten the gib screws, unless I'm actually using the top slide. The majuority of the cutting force is down rather than parallel to the lathe axis. I don't use the top slide to do parallel turning, that is done using the saddle. Instead I use the top slide to face a part to an exact length on the odd occasion I need to do so. So if the angle is out by a fraction of a degree it doesn't matter.

No idea what the zero-to-zero screwcutting method is, but I've never had a problem plunging straight in to the theoretical thread depth, plus a trial fit of course.

Andrew

On my first lathe, the power feed was the same drive train as the manual, only easier and more consistent.

With the Raglan LJ, I never used the manual long travel - firstly, it was not the most robust part of the apron and, ,secondly, why not use the separate (from the leadscrew) power feed provided? No point in having power feed and wearing out the leadscrew instead!

I see no reason to change for the 5”.

Top slide is where it gets put when it needs changing - and there it remains until I need it at another angle. On the first lathe, the long travel power feed was so imprecise that I often left the top slide set exactly parallel.

So, no real fixed ideas - I just use it as best suited for the job and machine! Why have fixed ideas when flexibility is better?

Surely it's nearer to 6 degrees (arcsin(0.1) = 5.74 degrees) for 10:1 on the topslide.

Harold Hall takes this one step further and in some instances advocates 0.573 degrees for 100:1 !

...but I'm in Andrew's camp** (and Martin Cleeve's) and even when threading just put the cuts on 2:1 for 55 & 60 degrees and 4:1 for Acme. The cross-slide gives a direct reading of the depth of the thread.

Jon

[Edit: ** Not quite then if he just does plunge cutting. By putting 1/2 of the cut on the topslide at 90 degrees it is equivalent to arctan 0.5 = 26.5 degrees and so close enough for 55 & 60 degrees. By putting 1/4 of the cut on the topslide at 90 degrees it is equivalent to arctan 0.25 = 14 degrees which is ok for Acme.]

Edited By Jon Gibbs on 12/03/2018 12:02:50

I'm not really sure what the whole point of setting the top slide over really is, like many have said, you can quite happily leave the top slide parallel to the bed and it still works.

The only useful implement to mention that should go with thread cutting is one of those gauges, you can line up your cutting tool with the square edge of the plate, held against the outside of the work piece and this ensures that the thread profile is being cut square to the work piece.

This corrects the angle in case you were slightly out to begin with. probably more important when it comes to internal thread tools or when it's harder to see if it's sitting straight. 

Michael W

Edited By Michael-w on 12/03/2018 12:38:10