Compound question

[Wheat.Millington]

I see a lot of people replace their compound/slide with a solid block on small lathes in order to improve rigidity. I'm considering doing this on my 1hp 12x24, but would there be any meaningful gain to just tightening the gib screws on the existing compound while it's not in use? It's easier to simply readjust the gibs than to swap in/out the copmpound slide whenever I want to cut tapers.

 

[ConValSam]

Both Robin Renzetti and Stefan Gotteswinter have excellent videos on YouTube explaining both the physics of a solid tool post and how they built them that will answer your question fully.

 

[mikey]

The idea of a solid plinth is to eliminate a weak link (the compound) in the chain as cutting forces are transferred from the tool and work piece down into the structure of the lathe. This greatly improves rigidity and boosts the performance of your lathe, including parting operations. The compound is really only useful for thread cutting and the occasional taper but the plinth will be used every time you turn on the lathe.

 

[woodchucker]

I use my compound a lot. I could not see eliminating one axis. I cut tapers with it, chamfers that can't easily be done with a form tool, I use it for threading as I advance the compound, not the cross slide. If you don't need it, certainly it adds rigidity, but if you are like many, you will miss it.

 

[T Bredehoft]

The "job" have now (self apointed) involves alternately cutting an 8º taper, Acme , (15º) and regular (metric) threads (30º). Couldn't be done with a solid tool block. I know, a taper attachment and plunging the threads straight in, but I wasn't taught that way.

 

[mikey]

It takes only minutes to remove a plinth and replace it with the compound for thread cutting and taper turning, then go back to the plinth for general turning. I wouldn't want to be without a compound either but the rigidity gained from a plinth is worth the minor inconvenience.

 

[woodchucker]

It takes only minutes to remove a plinth and replace it with the compound for thread cutting and taper turning, then go back to the plinth for general turning. I wouldn't want to be without a compound either but the rigidity gained from a plinth is worth the minor inconvenience.

I mostly tighten my gib screws when not using my compound. while not as rigid, I don't often find myself wanting more rigidity. I would consider it a pain to switch between the two. I'm lazy that way.

 

[graham-xrf]

It takes only minutes to remove a plinth and replace it with the compound for thread cutting and taper turning, then go back to the plinth for general turning. I wouldn't want to be without a compound either but the rigidity gained from a plinth is worth the minor inconvenience.

Mike, what is yours made of?
I mean, did you go for the vibration-dampening cast iron, or maybe for some kind of steel?
I expect you made it yourself. A picture might be nice
This is something I mean to try - but not yet. I have quite enough other fun stuff going on.

 

[mikey]

Mine isn't quite done yet. I've had a number of life challenges lately so it got put on the back burner. Mine is a big chunk of 6061, topped with a 1/4" thick precision ground steel plate. It has a ledge under the headstock side of the plinth that registers on the cross slide and once it is locked down it cannot move but it is simply bolted on so removing it and replacing the compound takes just a few minutes. The plinth runs the full width of the cross slide so I can rest my hand on it and also use it as a reference base for my tool height gauge.

The height of the plinth is a little lower than the compound height. This will allow me to get larger shanked tools on center a little easier. It will also allow me to bolt on a graver tool rest so I can use my gravers on my Super 11. My QCTP will be free to move. I prefer to change my lead angle at will, and this applies to both HSS and carbide tools. You would be surprised how well the end cutting edge of an insert works when the lead angle is altered from perpendicular.

I have a block of cast iron that will be a base for rear mounted tools. I plan for a parting tool back there and will also be able to mount my Eagle Rock knurler there, too. These and any other rear mounted tool will have their own holder that will bolt to the cast iron base; the base will likely stay in place and I'll just pop tools on it when needed.

Pictures when it's done, okay?

I should clarify that I've made and have used a plinth for a friend's lathe so I know exactly how good they are. My Sherline lathe's tool post also mounts directly to the cross slide and this works extremely well.

 

[T Bredehoft]

I keep a cut off tool mounted on and keyed in the left hand T Slot of my 10-30, I've moved it fore and aft occasionally to eliminate what seems like yards of cranking the cross feed. A changeable tool (knurl) would be handy, too.