Hi Jonathan,

Is there a saddle clamp? If so make sure you don't remove too much material. If you remove the wiper, is there still play?

Thor

As it's new refer back to the supplier.

Robert Butler

Does it matter?

On a prismatic bed side-play and accuracy depend on the upper rail (or rails). The saddle slides on the rails and is unlikely to lift in normal operation because the cutting forces go down through the saddle and into the bed. Thus the clamps underneath needn't be anything special in terms of fit.

There are a few jobs, like parting off with an upside down tool in a rear tool post, and milling in the lathe, that might lift the saddle. What are you doing when the saddle lifts? There might be another way of doing the job.

Prismatic beds were controversial when they first appeared. Flat bed owners thought they were inferior. Nonetheless modern lathes seem more likely to be made with prismatic beds than flat ones. Ages ago I think MichaelG linked a document that explained the pros and cons, but I can't remember what it said.

Dave

Edited By SillyOldDuffer on 20/05/2022 12:59:26

That is about the right amount of clearance for there. Much less and it will tend to bind. As SOD pointed out, the block is essentially a lift plate that comes into play only if using an inverted parting tool, or a boring bar sticking way out in front of the saddle, or the top slide extended far foward thus causing the saddle to tilt. If you do machine any off that block, you will have to add shims to get some clearance back again. Journeyman's linked page has some good info and ideas on it re that block.

I thought I recognised that lovely puce paint colour. See the thread that Michael Gilligan linked to in his above post re the adventures of one forum member's Optimum lathe. The lift-plate clearance was the least of his worries. Bed was bent like a banana by about 1mm from what I remember and machining was all-round pretty ordinary. But with a bit of fettling it became a useful machine and he has made a number of very nice working model engines on it.

Agree with Robert Butler, you say it’s new, why are you not complaining to the supplier instead of taking the thing apart?

I wonder if the OP has his numbers mixed up. Do they make a 0.01mm feeler gauge? That is less than half a thou' in old money.

Of that, I have no idea. Rightly or wrongly, one can only rely on what is posted. Might even be units mixed up as well, for all we know.

I reduced the saddle play by milling the "press boards" on both my lathes. The play left will be about 0.01 mm or less.

On the small lathe, I also added 2 spring loaded ball bearings. They pull the saddle on the bed if the load is not to heavy. If the load is to heavy, the old "press board" takes over.
If the bed is worn, you need more play but the bearings still pulls the saddle on the bed.

These changes improves the repeatability/accuracy, especially when doing shallow cuts.

Also the yearly maintenance takes a few hours less because the play doesn't need to be adjusted any more.

For the foto's view my album (Carriage Saddle Press Board)

For the description PDF

Edited By Huub on 20/05/2022 22:10:12

Edited By Huub on 20/05/2022 22:12:24

Edited By Huub on 20/05/2022 22:17:15

To the 'send it back' brigade,

Who are these, Dave? The closest I have seen is to refer back to the supplier – which is certainly not to just send it back.

It may be possible that sending it back is a total non-starter – depending on the seller.

The 0.1 to 0.15 mm gap is not the issue. There will be more problems than that underside block. You will be better off to take it apart and see how the saddle fits to the Vee way. Then correct that if needed. The rear bearing block is the one most likely to be experiencing any lifting, especially of rear tool posts are added. While taking the saddle off the machine, look at and clean out any of the oil lube drillings etc of swarf etc. Check and deburr things that need it. Some edges should be left sharp to act as a scraper , where a chamfer or radius will allow junk to work it's way in between the surfaces. Cleaning out the factory swarf or grindings is the biggest advantage of stripping down the hobby end of machine tools.

Neil