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The Artful Bodger
07-15-2014, 12:03 AM
My Chinese 12x36 lathe (type CQ6230A-1) has a very unsatisfactory cross slide lock that consists of a grub screw pressing on the cross slide gib. It is effective enough but it is in a very awkward place with the grub screw on the side of the cross slide right where it can not be got to if the tailstock is moved up.

So I thought of this modification which would put the adjusting screw on the top of the cross slide..

https://farm3.staticflickr.com/2899/14471683510_7fa367bfe1_m.jpg

As you can see screwing down the top grub screw would force a ball between two others and hopefully put pressure on the gib.


Any comments before I start drilling holes in my lathe?

John

RichR
07-15-2014, 02:02 AM
Hi John
Interesting idea. I think you will need to apply more force from the top screw compared to using the horizontal screw. Getting the alignment where the three
balls meet may take some fiddling.

Ian B
07-15-2014, 02:52 AM
John,

Looks like it'll work - as the 2 horizontal balls spread wider, force on the gib will increase. It might give so much force that something'll break.

For top access, you could also use a vertical shaft with a cam to actuate a plunger, that would also work.

Ian

SGW
07-15-2014, 08:08 AM
Interesting idea -- I may try it! I installed a cross slide lock on my South Bend 10K that simply replaced one of the gib screws with a small lever, and as you note, it ends up right where you can't get at it.

PixMan
07-15-2014, 08:19 AM
I've never seen a gib that lays flat on the bottom like that. All of them I've ever seen stand alongside the 30 or 45 surface of the dovetail.

DR
07-15-2014, 08:34 AM
Interesting idea -- I may try it! I installed a cross slide lock on my South Bend 10K that simply replaced one of the gib screws with a small lever, and as you note, it ends up right where you can't get at it.

One of my past machines had this setup from the factory. It's been so long ago, I don't recall interference with tailstock being an issue though.

Occasionally you'll see a lathe in a commercial shop with the compound and cross slide's gibs adjusted very tight to prevent any unwanted movement during turning. Usually so tight that in every day usage it's painfully hard to crank the handles.

Jaakko Fagerlund
07-15-2014, 09:34 AM
Hi John
Interesting idea. I think you will need to apply more force from the top screw compared to using the horizontal screw. Getting the alignment where the three
balls meet may take some fiddling.
Exactly the opposite, that arrangement forms a knee-joint which provides tremendous force, so I would be careful when tightening that screw.

RichR
07-15-2014, 10:37 AM
Thanks Jaakko, I didn't see it initially but the action is similar to a wedge.

RichR
07-15-2014, 10:41 AM
I've never seen a gib that lays flat on the bottom like that. All of them I've ever seen stand alongside the 30 or 45 surface of the dovetail.

You're reading the drawing wrong. It's a cutaway view and the gib is on the left. It's just drawn very thin and is difficult to see.

PixMan
07-15-2014, 02:35 PM
You're reading the drawing wrong. It's a cutaway view and the gib is on the left. It's just drawn very thin and is difficult to see.

Gotcha. Now I understand it, and think it needs a better design.

As shown, the ball directly below the "grub screw" would put equal pressure on both balls below it, so only half the pressure goes to the gib while the other half blows out the side of the cross slide. A better way would be to make a short cylinder of steel at the thread minor diameter, then grind or mill a 45 angle on the end. Align that 45 cut with the gib when you drop it on top of the ball. All the force goes one way.

Rosco-P
07-15-2014, 02:47 PM
How about one brass tipped setscrew on the opposite site of the cross slide? Other consideration is perhaps your gib is fitting poorly, causing you to have it adjusted more loosly just to get mooth travel, but resulting in more slop.

Rosco-P
07-15-2014, 02:54 PM
A better way would be to make a short cylinder of steel at the thread minor diameter, then grind or mill a 45 angle on the end. Align that 45 cut with the gib when you drop it on top of the ball. All the force goes one way.

A classic idea for a fast acting parts lock, right out of a jigs and fixtures design book. Even better, replace the setscrew with a cam action lever.

Jaakko Fagerlund
07-15-2014, 03:42 PM
Gotcha. Now I understand it, and think it needs a better design.

As shown, the ball directly below the "grub screw" would put equal pressure on both balls below it, so only half the pressure goes to the gib while the other half blows out the side of the cross slide. A better way would be to make a short cylinder of steel at the thread minor diameter, then grind or mill a 45 angle on the end. Align that 45 cut with the gib when you drop it on top of the ball. All the force goes one way.
Every force has to have an equal and opposite force, so it doesn't matter where it goes or what is behind it as long as it holds. In your suggestion that opposite force is against the pin/cylinder and in the OP case it is against the screw. Both provide the exact same result.

PixMan
07-15-2014, 03:47 PM
Every force has to have an equal and opposite force, so it doesn't matter where it goes or what is behind it as long as it holds. In your suggestion that opposite force is against the pin/cylinder and in the OP case it is against the screw. Both provide the exact same result.

The downward force against the wedge-tipped plug I suggested would be mostly against the ball (or a mating wedge), some would be straight down and a little to the opposite side. The force against the opposite side would have more metal if there was no through hole, less likely to blow out the side of the slide.

Jaakko Fagerlund
07-15-2014, 11:51 PM
The downward force against the wedge-tipped plug I suggested would be mostly against the ball (or a mating wedge), some would be straight down and a little to the opposite side. The force against the opposite side would have more metal if there was no through hole, less likely to blow out the side of the slide.
No, you just can't cancel the laws of physics. If the ball sees 100 N of force from the wedge, then the wedge sees 100 N from the ball. It just doesn't matter how you do the configuration, the forces will be the same, only the direction they act on can change. And it hardly makes a difference where that force is pointing, though best would be the exact opposite direction to the ball travel to get the most out of it.

The Artful Bodger
07-16-2014, 02:41 AM
It has been suggested that I should try 'rubberdraulics' using bathroom silicone rubber caulk which is probably worth an experiment.

dian
07-16-2014, 03:30 AM
what do you mean, putting silicone into the hole and a screw on top of it? how should that work, as silicone is very soft?

and jaakko is absolutly right.

The Artful Bodger
07-16-2014, 04:32 AM
Soft but not easily compressed otherwise that is the idea, fill the space with silicon rubber and screwing down the screw will put pressure on the gib. But I have not experimented yet.

Ian B
07-16-2014, 07:59 AM
AB,

I wonder if using kitchen silicone caulking would work better than grease in the old trick of hammering a close-fitting rod through a bearing in a blind hole to hydraulically jack it out - less leaks.

Ian

Toolguy
07-16-2014, 05:38 PM
I know modeling clay works good for that so silicone caulk probably would too.

The Artful Bodger
07-17-2014, 12:20 AM
https://farm4.staticflickr.com/3885/14487476299_37cdc62737_z.jpg

A block to test the idea of rubberdraulics.

The cap screw goes in the top hole and the piston goes in the side. The passage between them is filled with bathroom caulk which I will leave for a few days to set.

Lew Hartswick
07-17-2014, 06:52 AM
A block to test the idea of rubberdraulics.

The cap screw goes in the top hole and the piston goes in the side. The passage between them is filled with bathroom caulk which I will leave for a few days to set.
Way to go there bodger, There's nothing like a REAL test. :-)
...lew...

The Artful Bodger
07-17-2014, 07:00 AM
Hi Lew, I will need some way to demonstrate the pressure that appears on the head of the piston which will be a little, maybe 40%, more than the pressure from the cap screw but I have a day or two to think about how to do that!

mike4
07-17-2014, 07:04 PM
I would suggest a short cylinder at the front of the screw , otherwise the silicon will just chewup. also put some oil in the passages to stop the silicon from sticking to the metal .
You only want it to act as a medium to transfer the force from the screw to the piston.

Michael

The Artful Bodger
07-20-2014, 03:34 AM
I decided the caulk had had enough time so I tested the little test device. It was no surprise that it did work.

However, I doubt I would be using this for my cross slide lock but it is something to be kept locked away for future reference!

dian
07-21-2014, 09:46 AM
how well did that work? how come the compressible rubber transmitted the force?

cameron
07-21-2014, 11:34 AM
how well did that work? how come the compressible rubber transmitted the force?

Rubber is compressible in one direction if it can expand in one or more different directions. It has a very high resistance to being compressed in volume, as do most liquids and solids.

Rosco-P
07-22-2014, 11:23 AM
I decided the caulk had had enough time so I tested the little test device. It was no surprise that it did work.

However, I doubt I would be using this for my cross slide lock but it is something to be kept locked away for future reference!

So how will you proceed on this project? I'm guessing it's an outgrowth of the toolpost grinder project. Your desire is to lock the cross slide while using the compound free to traverse the grinder across the work.

The Artful Bodger
07-22-2014, 03:20 PM
Rosco, I have not decided on how to lock the cross slide. I may have to continue using the very awkward grub screw that works on the gib strip.