Follow Rest Modification

[Joe-R]

Hey all,

I thought I'd share a possible solution to an issue I've had a few times when needing a little extra support while turning and/or threading on the lathe.

I need to make a left hand threaded lead screw and the diameter will be too small and it will be too long to remain rigid while threading with a 10-TPI ACME insert, my first thought was to use the follow rest that came with my lathe but in most cases the follow rest never lines up behind the insert the way it needs to.
I like setting the compound at 14° for ACME threads and since it's left hand threads, the compound needs to be swung to the left and as the follow rest is now, it will be way too far to the left of the start of threads and the cutting tool so it just won't work without modifying something.

I've taken some time to model up what I think will be the solution and I captured a few renderings in Fusion to post here.
Sorry, I don't have any photos of the follow rest because I haven't actually done the machining just yet but if there's interest from anyone I'll take some photos along the way and post them here.

Note that I have added a third bronze finger that comes up from the bottom and that is only for threading in reverse (chuck spinning clockwise), in some cases I do thread in reverse, it just depends on the threading job.

At some point soon I hope to add some roller bearings to the bronze fingers, maybe when I make this mod?? Dunno.

Anyway, maybe this idea will help someone else and maybe someone can chime in to let me know that I'm not thinking of something that I need to think of before I cut this thing up

All the best!

Joe

 

[benmychree]

It looks like a good rational plan, but forget about the rollers, chips will get under the marring the work and causing inaccuracy by the part being forced out of alignment.

 

[Joe-R]

forget about the rollers, chips will get under the marring the work and causing inaccuracy by the part being forced out of alignment.

Good point!
Thanks for mentioning it.

 

[Jim F]

Why do some Co.'s put the follow on the left side ?
It need to be on the right side.

 

[Joe-R]

Why do some Co.'s put the follow on the left side ?
It need to be on the right side.

I think the reason that follow rests are on the left is because the cutting tool is on the left and the main reason for the cutting tool being on the left is so it can get as close to the chuck as possible.
In most cases the follow rest needs to be as close to inline with the cutting tool as possible.
I hope that makes sense.

 

[Mitch Alsup]

a) I don't think you will need the third finger to do a left hand thread. All you do is cut from the chuck towards the tailstock running in the chuck in the forward direction.

b) I think the dovetail will be a BIG source of vibrations (lack of stiffness)

c) the purpose of the follow rest is to prevent the part being machined from vibrating (See Abom79's last video--It is my conjecture that a follow rest would have saved his part.) As such, it only needs to touch the part close to where the cutting is being done--preventing deflection up and back.

 

[Joe-R]

a) I don't think you will need the third finger to do a left hand thread. All you do is cut from the chuck towards the tailstock running in the chuck in the forward direction.

b) I think the dovetail will be a BIG source of vibrations (lack of stiffness)

c) the purpose of the follow rest is to prevent the part being machined from vibrating (See Abom79's last video--It is my conjecture that a follow rest would have saved his part.) As such, it only needs to touch the part close to where the cutting is being done--preventing deflection up and back.

a) I realize that left hand threads are cut with the normal or counter clockwise rotation and away from the chuck but many times I do my threading for right hand threads with the chuck spinning in reverse or clockwise and thread from the chuck to the tailstock with the tool and insert upside down which pushes the stock back and DOWN.

b) The dovetail block will be made of 3/4" thick steel and there isn't that much load on the follow rest to begin with and as you say, it's just to prevent the workpiece from vibrating.

c) I am fully aware of the purpose of the follow rest.
In many cases there is a shoulder where the threads start near the chuck and a shoulder would prevent the use of a standard follow rest since the follow rest is not aligned with the cutter. If the follow rest is too far to the right, it would hit the live center at the end, I prefer the follow rest to line up with the cutter.
I also prefer to set my compound at 14° for ACME threads to reduce the chip load and thereby reduce chatter, meaning I don't want to set the compound parallel to the bed just so I can line up the cutter with the follow rest.
And who the heck is Abom79?

You seem to maybe think that I've never done any threading on a lathe before? I assure you, this is nowhere near my first time.

Have a nice day.

 

[Mitch Alsup]

And who the heck is Abom79?

One of the most respected (and nice) machinist on youtube.

 

[Jim F]

One of the most respected (and nice) machinist on youtube.

Not so much, lately......

 

[Jim F]

I think the reason that follow rests are on the left is because the cutting tool is on the left and the main reason for the cutting tool being on the left is so it can get as close to the chuck as possible.
In most cases the follow rest needs to be as close to inline with the cutting tool as possible.
I hope that makes sense.

The twins put it on the right side of the carriage, and they were smarter than I am.