using quick change post backwards

[monarch1973]

strange question. Has anyone used a quick change toolpost backwards? like instead of the force being applied to the post, it will be on the dovetails. ive got to turn some threads on 1 1/2" square, and its 81" long. Ive got my lathe maxed out length wise, and If I swap the tool to the right side of the post instead of left, I think I can do the job. Otherwise, I'll have to leave it long, and turn a groove towards the chuck, do the threads, and cut it down.

 

[FamilyTradition]

You will most likely be fine setting your tool in the post that way. You won't want to take heavy cuts anyhow considering the length of the part.

The big challenge will be supporting the middle of the workpiece well enough. Once you get away from the chuck or the tailstock you will be fighting chatter and deflection.

 

[BoxcarPete]

Wedge type? The amount of force applied between the wedge and the toolpost is at least an order of magnitude higher than your cutting force, otherwise the toolpost would not be stable in normal use. You probably will not notice the difference.

 

[monarch1973]

its an aloris piston type. Yeah I'm not looking forward to trying to get this thing all set up. I'll have to run really slow speeds to keep the chatter down. Plus, I've got to make a fixture so I can even use a steady rest with the square shape.

 

[monarch1973]

Wedge type? The amount of force applied between the wedge and the toolpost is at least an order of magnitude higher than your cutting force, otherwise the toolpost would not be stable in normal use. You probably will not notice the difference.

Its only like 3" of threads on both ends. I dont have to do anything to the middle of it. I hope to use a rest in the center, and I think I can just barley use a center in the end with my tailstock hanging a little ways out the back haha.

 

[moonlight machine]

It will be fine, done it many times.

 

[monarch1973]

thanks eveyone! i'll get to it.

 

[johnmontrose]

...I've got my lathe maxed out length wise...

Just a couple of ideas on this issue: turn the compound slide so the handle is facing the chuck and wind it towards the tailstock as much as it will go. That might also allow you to mount the tool so the cutting forces go into the post.

Use a standard RH boring bar pointing towards the tailstock as an OD turning tool for extra reach.

Philosophical question: what direction are the forces on the toolpost when doing standard ID boring with a RH tool? What direction are the forces on the toolpost when using a LH OD cutting tool?

 

[spaeth]

Might want to consider drilling and tapping a hole in each end and putting in a threaded stud. You could lock tight it and pin it if you are worried it would unscrew. My 2 cents.
spaeth

 

[atex57]

I made an offset tool block that sticks out to the right of the toolpost, kind of like how some KDK holders are made. Makes working on the end of long pieces easier.

Ed.

 

[BoxcarPete]

Just a couple of ideas on this issue: turn the compound slide so the handle is facing the chuck and wind it towards the tailstock as much as it will go. That might also allow you to mount the tool so the cutting forces go into the post.

Use a standard RH boring bar pointing towards the tailstock as an OD turning tool for extra reach.

Philosophical question: what direction are the forces on the toolpost when doing standard ID boring with a RH tool? What direction are the forces on the toolpost when using a LH OD cutting tool?

Flipping a regular boring bar around in the toolholder will give you an LH OD tool.

Forces on the toolpost with a LH cutter on the left side will be much the same as an RH cutter on the right side. Maybe some subtle differences due to carriage rock, asymmetrical backlash on the apron rack, etc. but fundamentally similar.

 

[johnmontrose]

Flipping a regular boring bar around in the toolholder will give you an LH OD tool.

I am not sure what point you are trying to make. He is looking to thread something longer than his lathe will comfortably accommodate. Using the boring bar in this way, you can remove the tailstock, drive the saddle to the right as much as possible, have a fixed steady on the headstock side of the saddle and use the stick out of the boring bar to have the cutting tip past the end of the bed if necessary.

An old-style boring bar with a HSS toolbit poking out of it at right angles does not care in which direction it cuts, you just have to grind the toolbit correctly (in this case a 60 degree threading bit). It is the same as doing a blind internal thread by starting at the bottom of the hole and working outwards.

Forces on the toolpost with a LH cutter on the left side will be much the same as an RH cutter on the right side.

For clarity, by RH cutter I mean one that cuts towards the chuck (most commonly used) and LH cutter to mean one that cuts away from the chuck. If you mount a RH cutter on the right side, you limit how close to the chuck you can cut so I always mount mine on the left. Forces on a LH cutter on the left side will be opposite those of a RH cutter on the left side.

If you have a left hand boring bar cutting towards the chuck, do you put the toolpost on the back side of the stock and mount the bar at the front? No, of course not. You mount it in the same place as a RH bar, just with the pointy bit that produces the chips facing towards the back.