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Mini-lathe saddle casting error.

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modeng200030/12/2021 16:17:07
340 forum posts
1 photos

I recently bought a fairly cheap mini-lathe and all seemed as expected, that is it needed a going over to set up the various adjustments.The first time I face turned a bar the result wasn't as expected. The surface is convex and the error from flat is of the order of 0.5mm in 100mm. I believe it is normal for there to be a slight deviation from flat but this is excessive.

Without any machining facilities to correct the saddle is there anything i can do to reduce the error? The top slide cannot be positioned to do the final surfacing so that I can finish this job. I only have hand tools available so am I right in thinking the best solution would be to replace the saddle?

John

JasonB30/12/2021 16:48:48
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25215 forum posts
3105 photos
1 articles

A tiny amount of Concave is said to be acceptable but not convex.

First thing would be to contact the supplier assuming you bought it new.

RobCox30/12/2021 16:53:25
82 forum posts
44 photos

Firstly, any deviation should result in a concave surface, not convex. 0.5mm in 100 sounds terrible to me.

It's not necessarily the carriage or cross slide that's at fault here. It might be that the headstock isn't parallel to the ways.

Correcting this isn't as simple as clamping it on a milling machine or grinder and having at it. Firstly an exhaustive examination of all the parts mentioned above would be in order to determine which part(s) are at fault. Next, removing metal from the saddle v ways would alter its height, resulting in less engagement on the carriage rack. If it's the headstock at fault the tailstock would need attention too.

You might have to decide if it's worth trying to fix as without the required expertise you might make it worse and write it off. If it were bought new I'd be angling for a refund or replacement.

Rob

Pete Rimmer30/12/2021 17:12:57
1486 forum posts
105 photos

As Rob says first check that it turns parallel by turning a part held only in the chuck. If that is acceptable, then it's time to look at the saddle's cross-slide way closest to the chuck.

Edited By Pete Rimmer on 30/12/2021 17:13:21

john fletcher 130/12/2021 17:45:32
893 forum posts

A friend very recently bought a small lathe and had a similar problem . Apparently under the saddle are two screws which were very loose, fortunately another friend turn up and he had exactly the same problem when he bought his small lathe. I'm told they need going over and tweeking before use, otherwise good for the price. John

modeng200030/12/2021 19:15:40
340 forum posts
1 photos

Thanks for the wise words. I have checked that the lathe turns parallel so that is why I believe it must be the saddle. Using a square against the crosslide side shows an out of square similar to the measured error. The crosslide and saddle sides check as true rectangles.

John, I'll have a look for these screws but I haven't noticed them before. If they are not present then I guess it's back to the supplier.

John

modeng200030/12/2021 19:45:59
340 forum posts
1 photos

A bit more measuring and I find that the saddle topslide register is not parallel with the side of the saddle, the error being such as to create the convex turning. The saddle side is at 90 degrees to the lathe bed. Deduction is that the saddle has been machined incorrectly.

John

MikeK30/12/2021 20:35:27
226 forum posts
17 photos

As mentioned, check the headstock, which is something you can easily adjust with shims. The procedure I used, I think, was from the Yahoo mini-lathe user group...which of course is DOA, but I believe all of the files and such have been moved to the mini-lathe group on the groups.io site.

modeng200031/12/2021 06:59:29
340 forum posts
1 photos

Thanks Mikek, I believe the headstock is true to the lathe bed.

John

modeng200031/12/2021 15:48:13
340 forum posts
1 photos

I have sent the requested photographic information. We wait to see what happens next.

John

not done it yet31/12/2021 16:23:39
7517 forum posts
20 photos
Posted by modeng2000 on 31/12/2021 15:48:13:

I have sent the requested photographic information. We wait to see what happens next.

John

That smacks of a chinese supplier. Typical of them to request photograhic evidence - even of missing parts.🙂

modeng200031/12/2021 19:22:56
340 forum posts
1 photos

'That smacks of a chinese supplier'

Yes, but I suppose it is not unreasonable. There are those around who like to try their luck.

Anyway I'll go along with them for now.

John

modeng200001/01/2022 14:40:03
340 forum posts
1 photos

The next chapter:- they said they were not able to see the error using the photographs I sent, or so they said!

Now they are asking for a video. I'll go along with this and see what they ask for next.

John

Chris Trice01/01/2022 15:19:50
avatar
1376 forum posts
10 photos

Put a straight edge across the surface and slip a feeler gauge between the part and the straight edge. That should tell the story.

John Haine01/01/2022 15:38:46
5563 forum posts
322 photos

Some further information would be useful. What type of lathe is it, the generic mini-lathe? What badge does it bear? Did you buy it new, and who supplied it?

A lathe with that degree of error is not fit for purpose. If you bought it new in the UK then the supplier should replace it or refund your money. It is likely that the supplier will be concerned about making further sales to amateurs, so please name and shame them on here. Finally, if you can post the photos you took then maybe we can recommend a better process for taking meaningful pictures to prove the problem. Frankly I can't see how a video helps except in kicking the can along the road a bit further in the hope that you will give up.

And if the lathe was bought new the DO NOT make any attempt to fix the problem which would be an excuse for wriggling out from any warranty.

Oldiron01/01/2022 16:12:45
1193 forum posts
59 photos

I agree 100% with John Haine above. If UK supplier give them a call as they should be your first point of contact. And DO NOT try any repairs until you have exhausted all avenues of warranty and returns.

regards

modeng200001/01/2022 20:24:31
340 forum posts
1 photos

Thanks all for the continuing advice.

At this point I'm not going to give details of the make or supplier of this lathe. As I wrote at the begining, it is a low price mini lathe and I expected to have to make adjustments. However there is no adjustment for this fault.

It is fair to give them the chance to provide a solution. If that is not forthcoming then perhaps is the time to identify.

John

modeng200003/01/2022 14:36:14
340 forum posts
1 photos

Have received a reply to my videos expressing regret that the machine is not up to standard.

Have been offered a replacement machine and no need to return the old one. I am left wondering what the word machine includes, perhaps just the rep[lacement crosslide machined casting.

Time will tell.

John

modeng200007/01/2022 19:59:25
340 forum posts
1 photos

I am very pleased to have a resolution to the faulty saddle problem. The company has recompensed me and now that I have an accurate machine I can perhaps get on with the job that showed up the error.

John

Roger Knill26/01/2022 22:49:29
1 forum posts

Glad you got it resolved.

would be interested in finding out what lathe it was and who the vendor was. You hear a lot of stories of poor quality and poor customer service, it’s good to hear of a seller willing to put right mistakes that do happen. Did they replace the whole lathe or just the saddle?

thnaks

Roger

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