Lathe Dogs

[Hukshawn]

That video was surprisingly informative.
Learn a bit more each day. Just wish I had more time behind the machine.
Thanks guys.

 

[SoIll914]

Not only is it useful its also easy(for me anyway) to set up even on my benchtop 9x19. I like getting to use the power feed for more uniform surface finish. the only thing that really bugs me is the chip rats nest when it runs into my dog and starts flying everywhere. It seems the main drawback i hear of is the pain it is to precisly recenter the tailstock after youre finished

 

[Hukshawn]

Not only is it useful its also easy(for me anyway) to set up even on my benchtop 9x19. I like getting to use the power feed for more uniform surface finish. the only thing that really bugs me is the chip rats nest when it runs into my dog and starts flying everywhere. It seems the main drawback i hear of is the pain it is to precisly recenter the tailstock after youre finished

Why would you need to recenter the tail stock? why would it move?

 

[SoIll914]

Right now im making a double end taper to throw a drill chuck on from my craftsman drill press. MT2 and J33. So i offset the tailstock. I tried compound taper turning and i did not like it. more cons than pros for me.

 

[Hukshawn]

How do you calculate the offset for the taper?

 

[British Steel]

How do you calculate the offset for the taper?

Not that complicated, if you're working in taper per foot measure the part length between centres, say 15", divide that by 12" (so 1 & 1/4) and multiply that by the taper per foot THEN HALVE IT as your tool is only cutting half the taper (the other side is away from you on the back of the part) - this will get you close, then if e.g. it's a Morse taper you're cutting, blue the part and try it in the Morse socket to check, adjust the tailstock a fraction of a gnat's wotsit if required as this will be subject to a (small) Cosine error. OR calculate the angle from the taper/ft, halve the angle and offset by the Sine times the length (a bit like how you'd use a Sine bar). Easier to blue and adjust, IMHO!

If you're working from an included angle, multiply the length between centres by the Sine of half the angle, which is effectively converting to taper/ft.

I've found the best way to set the tailstock offset is to first of all *get it centred precisely* then set a dial indicator against the tailstock barrel, adjust as required.

Hope that helps, not confuses!

The other great use for turning between centres, one of my favourite get-me-out-of-troubles, is the between-centres boring bar - the workpiece is held on the carriage (T-slots help!) and a bar between centres carries the cutting tool, ideal for boring oddly-shaped parts (engine cylinders f'rinstance) and guaranteed to give a true cylinder without any bell-mouthing or eccentricity/ovality. A good trick is to put a turned-up centre in the 4-jaw opposite the tailstock, dial indicator on the toolbit, make bore adjustments by tightening/loosening opposite chuck jaws to increase the cutting radius (you can take the BC boring bar out to measure the bore, like turning BC it goes back in *exactly* the same place) - a bit oldschool, but it works!

With a bit of ingenuity you can even set up horizontal milling cutters on a between-centres bar...

Dave H. (the other one)

 

[SoIll914]

One thing i learned after trying many times to turn a mt2 taper is 60 degree center drilled holes for supporting the stock between centers will throw off your taper when its finished. Ive seen pictures of the guys using ball bearing looking centers but have not tried this myself. it was frustrating to figure out but dont give up!!

 

[Wreck™Wreck]

While waiting for the heavy weights to shed some light, in my humble opinion any work that needs extra support from a TS centre, should be held between centers. Short work can be held in the chuck only. Situations where anything else is required should be dealt with on an individual basis.

In Tom's video, maybe the wobble is severe to make a point but doing a job like that would be a last resort for me. I would not make a habit of it for sure.

Not always true, tubular parts may be held internally with a chuck whilst held by a plug on the tail stock end, solid parts may be held in a chuck and tail stock to great effect and may be turned closer to the head stock end without the dog being in the way.

If one is concerned about the part walking in the jaws just turn a pocket in soft jaws for the job at hand.

This is a 6 1/2" OD 64" long steel tube held internally with a chuck and a plug that I made for the tail stock end, held .003 the entire length and the finish was excellent. At this size anything closer is best done on a cylindrical grinder.

 

[Tozguy]

Wreck, thanks for giving us an example of the variety of ways we have of holding in the lathe depending on the circumstances. Might I ask what kind of chuck that is in the picture?

The idea of grinding a pocket in soft jaws is duly noted for posterity.

If something in my statement is not always true then sometimes it is. But I'm not sure exactly what you are referring to.

Shawn might have by now the info he wants about lathe dogs but when and how to apply different methods of work holding to avoid dogs is related. Here is another tool to consider:

 

[benmychree]

When held in the chuck, as the workpiece rotates, any eccentricity in the holding of the work in the chuck jaws is exacerbated by the work being held centred at the TS end. So as the work rotates it tends to "rock" in the chuck jaws and "walk" around, becoming loose and marring the surface.
Hope I didnt make that more confusing than it sounds.............

Cheers Phil

I can relate to that; when I was a apprentice, one job I had was to face, center and groove the ends of 5" shafting 15 ft. long; we had only one steady rest, and the sag in the shaft when facing the ends and centering caused the shaft to travel endwise, outwards in the 4 jaw chuck, and also to travel endwise when cutting the slots near the ends of the shaft, using the tailstock to support the work; it generated so much force that it forced the tailstock back, even with 4ea 1" plus bolts holding it down, this in a 36" swing lathe. This was finally eliminated by laying 4 pieces od approx. 1/2" diameter round stock crossways in the chuck jaw grooves that allowed the shaft to rock and relieve the tendency to walk out, and yes, the shaft was supported about half the way along by the steady rest.