Fixing the Mini Lathe Saddle - Down the rabbit hole - Part 3
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- Опубліковано 13 лют 2024
- Continuing to tune up the Chinese Mini Lathe, next job to look at is the lathe saddle.
I have had a lot of problems with surface finish and the tool cutting on the outfeed. In this series we're working through the various problems with the lathe saddle as it came out of the factory and working out how to improve its accuracy and rigidity.
In part 1 we looked at the problem, take some measurements and start to hand scrape the bearing surfaces of the saddle in order to start to bring it into truth.
In part 2 we identified a problem with the alignment of the saddle bed ways which we need to sort out before we can move onto the actual gib strips.
Here in part 3 we refine the saddle gibs themselves and start to re-assemble the lathe. Optimism for a swift conclusion of the problem is high, usually a bad sign 😂
The fix applies to the following lathe models: CJ0618, Crenex 7"x14", Clarke CL300M, Warco Mini lathe, Sieg C2 and many other brands which are based off the Chinese mini lathe design. However the techniques could be applied to other makes, models and sizes of lathe and aren't limited to this particular model.
See part #1 here - • Fixing the Mini Lathe ...
See part #2 here - • Fixing the Mini Lathe ... - Навчання та стиль
What a shame. With a little more care and attention these mini lathes would be providing thousands (maybe tens of thousands) of people countless hours of fun, productivity and enjoyment. But the word is out that they’re trouble. Even armed with knowledge, skill and the right tools it’s a time consuming job that is frustrating at the very least. Imagine how many people simply don’t get into machinery work because they can’t start small and build their skills. These mini lathe machines should come in a complete kit form except that they should be machined to closer tolerances. It would probably cost the company the same amount to machine it correctly and just not assemble it. They win and we would certainly win. Most people who buy machines like this don’t mind fine tuning them but almost nobody wants to have to machine their own parts and rebuild them just to see if the hobby will lead to more. My hats off to you for your patience and persistence in going through this process.
Thanks David, I totally agree. I was lucky enough to be trained in a machine shop during my apprenticeship so I'm happy to fix any problems that I find, but as you say for the newcomers looking to pick up the skills on their own these lathes are a setback for them. I don't think all of the lathes are terrible, and it probably pays to buy one from a brand such as Clarke or Warco here in the UK. At least that way there will be a warranty and I'd like to think that if they are putting their names to the machines they would do more QA than the unknown brands.
I’ve had the same problem with the saddle binding the cure is to scrape the underside off the ways as they are not consistent with each other on both the front & back ways
At 5:00 your word "SPINNING" is actually called "HINGING" by professional scrapers. Just thought you would like to know. Thanks for taking the time to make this presentation.
Ok I'm legitimately invited now.
You're going to want a straight edge to measure against each face, and find a reference face that is actually straight. (We're not talking about a ruler, but a precision flat and long edge). Most hobbyists make their own.
From there you'll need to make that reference surface as flat as you can.
After that, you'll need to start measuring against the other surfaces and make them parallel to the reference surface.
It's a ton of work but there's really no way to cheat around it.
Here's a good video on what you'll need to do
ua-cam.com/video/7MTHWuS5S8A/v-deo.htmlfeature=shared
You'll want to think long and hard and the order of operations here, as doing things out of order will mean more work.
My suggestion would be to scrape the top of the ways flat first, that'll be your reference. Then scrape the underside of the ways flat and parallel to the top. Use a surface gauge and some blocks to prop the bed up to get your measurements on how to correct the angle.
Then measure the V ways using a similar cylindrical V block and determine how to correct their angle and scrape them parallel. (Side note, mark a point on the V cylinder so you're always measuring to the same reference, and cut a relief inside the V cylinder instead of scraping all of it - you only need 4 points of contact. In fact you can even use a bit of pipe instead of a solid round bar.)
Considering that none of the ways are hardened, don't put too much effort into it as they're sure to wear.
It also might be worth it to anneal the entire casting as they're likely not stress relieved either. Some time in the oven at the correct temperature will do it, but if it's in your kitchen you would probably want to clean and remove all the paint first else your cookies will never taste the same again.
Also, make sure you buy a big box of tea first, because it's sure to take a while.
Did someone say "Tea"?
I currently have one of mine (the one that's not getting a CNC conversion) in pieces for just such a rabbit-hole-dive... also going to hang a DRO (a "real" one with linear scales) off of it.
Good luck with it mate - DRO will be a great mod 👍
Hello Richard, I'm following with interest your enlightening videos, and trying to follow your tips in order to better tune my mini lathe, so I'll take the freedom to ask your advice from time to time, hoping not to bother you too much 😊
A couple of questions, then... First, is your scraping tool homemade or else is a commercial product? I'm asking this because at the hardware stores I asked for (I'm from Italy) they gave me weird looks 😆 Maybe it is not such a common tool?
And second, I noticed that someone around is suggesting brass as gib material... What is your opinion on that matter?
Thanks so much!
Roberto
Good to see you again Roberto! Feel free to ask as much as you want, the purpose of my channel is for people to share what they know 👍
Engineering hand scrapers are hard to find these days, not many people sell them. Mine was purchased from a UA-camr named "Impractical Engineer" - he makes and sells the scrapers on eBay - www.ebay.co.uk/itm/334369762367.
You can also try to search for Sandvik Coromant 620-20 though these are also hard to find. www.sandvik.coromant.com/en-us/product-details?c=620-20%20%20%20%20%20%20%20%20%20%20%20%20%20%20H10
Alternatively you could grind a scraper from an old file. 60mm radius on the end, 5 degree negative rake (95 degree blade angle).
Brass can be used for gib strips though I would prefer phosphor bronze. Cast iron gibs seem to be popular, as it has excellent sliding characteristics with itself. I plan to make some new gibs with phosphor bronze in the future, will probably cut them from hexagon bar as that way two of the sides will already be the correct angle.
@@radboogie
Thank you Richard! Only, I'm not sure to understand the advantage of using an hexagon bar as starting shape (my fault... 😊)
Being the cross slide gibs shaped as four-sided parallelograms (if I see them right), then is the hexagon choice a way to get precisely 120°/60° angled gibs, or else just a way to start with two surely parallel opposite sides, (that could be obtained also from a square/rectangular stock) and then work them to the desired (arbitrary) final angle?
Pardon me for possibly naive questions, but I'm into turning just for four days 😬
A long way to go...
Using hexagon bar is just my idea of being able to start with two sides at the correct angle. When I make new gibs I will be making them with hand tools (no milling machine) so if I saw a strip of hex bar leaving two sides at 60 degrees to each other, I can then file the opposite faces to be parallel with them and verify on my surface plate for parallelism. As I say, just an idea I had to improvise with hand tools.
How do you ensure that the scraping won't raise burrs that interfere with bluing?
You go over it with a fine stone and a bit of mineral spirit after scraping.
I think i would try cutting a long bar and check for taper. It might give you a clue as to wether the front way is parallel to the chuck. I dont mean to tell you how to suck eggs.
Thanks for the suggestion Mike 👍