Lathe solid tool post mount thoughts

[SouthernChap]

The real issue I see with the 7X Chinese lathes is that they are essentially a 5" lathe that has been biggined up. Ie, there's an extra inch of height baked in that really does not suit the design so they can claim its a "Bigger" machine. So the U is bigger and more flexible overall than it should be.

I made a plinth for my 5" Prazi and gained nothing but an art installation for the wall behind the machine.

My compound is low enough that just tightening the gib screws is sufficient, on the 7X....not so much.

This is a really insightful observation and it's based on experience of what was almost certainly the base design for the Chinese 7x machines, which gives it extra weight.

The negative effect of the extra inch on the radius of the swing on the Chinese mini lathes isnt something I've heard mention of before, but really does make sense and explains why the hobbymat/prazimat machines do seem to display somewhat greater rigidity despite not being that much more massy.

The hobbymat/prazimat machines are constraining the user to work within the constraints of the design as opposed to the Chines 7x's apparently adding an extra capability that actually ends up reducing their capability.

Every day is a school day; thank you.

 

[Provincial]

I have not heard of anyone complaining about the Craftsman 12" version of the 10" Atlas lathes, even though the 10" Atlas wasn't all that rigid. They just raised the spindle bore and tailstock by an inch.

 

[SouthernChap]

I have not heard of anyone complaining about the Craftsman 12" version of the 10" Atlas lathes, even though the 10" Atlas wasn't all that rigid. They just raised the spindle bore and tailstock by an inch.

I'm not sure you're comparing apples to apples here.

As I understand it, a 10x lathe is likely to be in a different league of mass (and thus rigidity) to even a Prazimat/Hobbymat lathe, let alone the Chinese 7x machines.

Besides, I'd reckon adding 20% to the cruicial dimension of a part of a lathe that is critical to rigidity (especially one that is probably only just on the good side of the line) is rather different to adding 10%.

 

[bill stupak]

On the Craftsman 12" (I have one) the ways are 1/2" thick, I believe all the smaller ones have 3/8" thick ways. As far as rigidity of the 12" when I make an interrupted cut I can feel and see the carriage and cross slide moving up and down.

 

[Dabbler]

@dml66 This modification has been done by several guys in my home town. They report varying levels of improvements from minor to fantastic.

I'm too far away to make one for you - but if you have an AXA or 0XA, you just need to get some 3 or 3 1/2 " round stock, cut off to longer than 1.55". You can face both ends to length, and drill/bore a centre hole. Mount your current tool post on top, and you should get an idea of how much it helps. Refinements can come later.

You do know since you have a QCTP, that the dimension isn't critical. 1.4-1.7" thick would be just fine.

There are plenty of members in Washington that probably have an off-cut that they can give you.

 

[dml66]

@dml66 This modification has been done by several guys in my home town. They report varying levels of improvements from minor to fantastic.

I'm too far away to make one for you - but if you have an AXA or 0XA, you just need to get some 3 or 3 1/2 " round stock, cut off to longer than 1.55". You can face both ends to length, and drill/bore a centre hole. Mount your current tool post on top, and you should get an idea of how much it helps. Refinements can come later.

You do know since you have a QCTP, that the dimension isn't critical. 1.4-1.7" thick would be just fine.

There are plenty of members in Washington that probably have an off-cut that they can give you.

Thanks Dabbler!

I found a piece of 3"x3"x1.5" thick ground low carbon steel stock at McMaster-Carr, also bought 1/8" and a 3/32" thick pieces, both 3"x3", just in case I end up a tad short for a particular tool in the QCTP holder, they'd act like shims.

 

[Dabbler]

Generally they will arrive slightly over length, for clean up. You will have to face them at both ends, as they will be saw cut. It should clean up to about 1.5" or slightly over.

 

[dml66]

Generally they will arrive slightly over length, for clean up. You will have to face them at both ends, as they will be saw cut. It should clean up to about 1.5" or slightly over.

These are considered ground sheets, the top and bottom do show swirls from the grinder, not a mirror finish by any stretch but probably no worse than I'd end up with if I faced it. The edges do appear to have been saw cut. Thickness is true to nominal.

 

[Dabbler]

Getting good contact is essential to having a rigid tool post. Even if you have to go a couple of thou short, you need that solid metal on metal contact.

Those are not usually grinding marks. These blanks are cut using a large circular saw. the contrary direction marks might be from a disc sander to improve flatness. They are too small to be Blanchard ground - unless these are Blanchard ground flat, then sawn to size.... (possible, but a costly way to do it)

Do you have a piece of float glass or surface plate (countertop granite won't do). Then put a sheet of 2000 wet and dry on the flat surface and lightly take off the saw/grinding marks. This will improve your contact significantly. Only take a tiny bit off the tops of the marks until you see a new surface over most (75-80%) of the surface.

When/if you learn scraping, the same principle applies.

 

[RaisedByWolves]

I'm not sure you're comparing apples to apples here.

As I understand it, a 10x lathe is likely to be in a different league of mass (and thus rigidity) to even a Prazimat/Hobbymat lathe, let alone the Chinese 7x machines.

Besides, I'd reckon adding 20% to the cruicial dimension of a part of a lathe that is critical to rigidity (especially one that is probably only just on the good side of the line) is rather different to adding 10%.

Thanks for this, I was too lazy to do the math.

You’re also talking about a machine that has larger ways and a wider overall compound in relation to its height.