Is the majority of mini lathe information on the internet bad?

[S. Heslop]

I haven't really adjusted my lathe since getting it out of the box, ignoring alot of what you read online (to take it apart and reassemble it). It worked pretty well at first but I guess after 3 or 4 years it's gotten pretty sloppy and i'm having a hard time getting a decent finish on any steel.

So I spent last night reading stuff on mini lathe modifications to see what other people have done and was kind of surprised by the amount of people saying to do stuff like wipe grinding paste over the bed ways to lap them. Now I might be wrong but that seems like a really bad idea for several reasons.

Other people are taping wet and dry paper to their bed ways to grind the underside of the carriage which also seems like a bad idea since you wont really be getting even wear, leaving any results up to chance.

In my head I really want to moan about mini-lathe.com since that seems to be where people are getting the idea for all this stuff from (plus the website really threw me for a loop when I first started out, especially with the guy trying to sell plans and guides for stuff that's freely available elsewhere), but i'm not sure if my reasoning is really correct. Am I right in thinking that those procedures are stupid?


However I am aware that there's loads of great information for lathes online, but usually aimed towards the real larger machines. I figure anyone serious about turning would just buy a good second hand lathe instead, and I wish I was more aware of that back when I bought the mini-lathe.


Anyways here's some pictures of my lathe with the carriage disassembled.



I'm planning to shim the saddle gibs for a tighter fit, and also figure out how to get the dovetail in the cross-slide to give proper contact. I might even go as far as to make a cam lock for the tailstock.

[chipenter]

I would not use grinding paste as it goes on working long after you think it's finished , scraping is the best method and a very usefull skill to learn , scrapers are very easy to make from an old file , those Chinees lathes have a hardend bed and will be to hard to scrape .

[Pete.]

Don't wipe your bed with grinding paste - that's the stupidest advice imaginable. Ditto for taping the abrasive paper to it to 'machine' the saddle. All it will do is increase what wear there already is.

[S. Heslop]

I'm glad I was too lazy to follow that bad advise all those years ago when I didn't know any better!


Spent the rest of today trying to get the cross slide gib to ride flat. I had the same problem as in this thread http://madmodder.net/index.php/topic,5406.msg57014.html#msg57014

Although I didn't have much success. I think the gib might just have another face worn into it. I've ordered some engineers blue to try checking that.

I might be entirely wrong but what I think is happening is something like this (my gib is a much better fit in it's space and wouldn't have room to slide downwards like in the crude diagram;



Where the screw is contacting the side of the hole and pushing the gib strip in the direction of the arrow. My plan was to mark the gib strip with felt tip pen, offset it a bit from the original screw holes, and let the screws contact the metal and mark where they touch. I then drilled new holes offset the other way to push the gib into the lower corner.



But it didn't quite work. Maybe it'd be better to drill larger diameter holes (and not as deep) so the screws can reach the bottom, and the tip pushes against the gib strip. Or maybe i'm entirely wrong about what's causing the gibs to tip. Or maybe the gib strip really does have a second face and that's why it doesn't sit flat. The uncertainty makes me hesitant to drill any more holes.

[vtsteam]

I kinda thought it was always just a dimple and centered and drilled in line with the screw hole (horizontally). That way the point contacts the end of the dimple and pushes the gib only horizontally. At least that's how I did it when I built my lathe.

And although fellow madmodders have recommended against using grinding paste or sandpaper on the ways, and one even called it stupid, I must disagree, and firmly state that it is in fact an excellent way to introduce needed chatter on ways which have been ground too finely, or worse, scraped. If there is excessive chatter, of course, a light wipe of epoxy will cure it. Try to work the epoxy in by sliding the carriage and tail stock back and forth before it cures. A dab or two on the leadscrew helps use up any excess and will quiet  a lathe permanently.

(In case anyone takes this seriously, the majority of the above internet mini-lathe information is bad.)

[Stilldrillin]

Hi Simon.
Yes. There are many out there, too confident of their own superiority.......

I have now owned 3 Mini machines.
First job, has been to remove and straighten the gib strips. (Bash with lead tup. Check, on granite floor tile).
All gib screw points filed, in the lathe, to a "drill point angle".

Never had any bother in 10 years.......

My carriage rocked, as the V was poorly milled. I filed the centre section, until it contacted at either end of the V.
This gave it three point contact. Which has never been changed.

The later retaining strips, http://madmodder.net/index.php?topic=6423.0  have never been adjusted, in 3 years....... 

David D

[S. Heslop]

I kinda thought it was always just a dimple and centered and drilled in line with the screw hole (horizontally). That way the point contacts the end of the dimple and pushes the gib only horizontally. At least that's how I did it when I built my lathe.

And although fellow madmodders have recommended against using grinding paste or sandpaper on the ways, and one even called it stupid, I must disagree, and firmly state that it is in fact an excellent way to introduce needed chatter on ways which have been ground too finely, or worse, scraped. If there is excessive chatter, of course, a light wipe of epoxy will cure it. Try to work the epoxy in by sliding the carriage and tail stock back and forth before it cures. A dab or two on the leadscrew helps use up any excess and will quiet  a lathe permanently.

(In case anyone takes this seriously, the majority of the above internet mini-lathe information is bad.)

Had a good laugh at this post.


Here's what I tried today though.


Used marker again to see where the screws contacted.


And drew gentler dimples.


But still no luck.


The gib is starting to look beautiful with all these holes. I tried turning the gib strip (poking a bit out from the carriage at this point) with a spanner gently to force it into position and seeing where the screws contacted with it like that, but that made the results even worse.

I feel like the set screw holes would work better a bit lower maybe, but there's not really much space left on the carriage to drill more screws. I suppose ive pretty much tried out ever possible hole position for the screws so far and none have worked out.

[Pete.]

I think he problem is that they have milled the slide with a huge gap and used a huge gib to fill it. It should be a lot more tall than it is thick and yet yours seems to be about square in that respect.
Not sure how I'd go about fixing that. One way would be to make a shim to glue on top of the gib to stop it lifting. Another would be to clamp the gib into the dovetail where it lives then drill through the screw holes to about 2/3 depth and make some dog point adjuster screws.

[John Rudd]

A friend of mine had the same issues with gib strips on a machine supplied by a well known tool merchant.....he was so disgusted with the quality of the machine he returned it.......
On my Sieg machine I replaced the gibs with brass variants. Been ok so far....

[DavidA]

Looking at the above picture,  there does seem to be something completely wrong about that strip. Non of the angles seem to match.

Maybe best to make a new one.

Dave.

[loply]

I have to say, having owned a mini lathe and having reconditioned numerous vices, sliding parts, scraping tools etc using a Biax, I agree with the grinding paste method.

I used it on my mini lathe and it made things a whole lot better. The gibs by default are usually mis-cut and not touching in more than one or two spots, after a few minutes of grinding you can blue them again and they will be spotting all over.

Take the saddle for example, the underside of the bed was too tight in some places and too sloppy in others where the gib rode. Couple of quick swipes with some grinding paste and an attentive set of senses to decide when it's just right and suddenly the saddle is smooth everywhere. You could scrape it... but it would take 5x as long, and is barely worth it on a mini lathe.

[S. Heslop]

Looking at the above picture,  there does seem to be something completely wrong about that strip. Non of the angles seem to match.

Maybe best to make a new one.

Dave.

Unfortunately I don't have a milling machine, so i'm quite limited in what I can do. I doubt i'd be able to hand file anything that's better than the original gib.

I suppose I could order some brass strips. But at £21 from arc euro trade, and no guarantee they'd work, it'd be a last resort. I've got very little money left, and in the back of my mind I want to replace this lathe entirely at some point anyway!

But yeah looking at the gibs on bigger real lathes, they tend to be very slender when this one is about a rhombus.


I figure my best bet is to try position a dimple like this or above;



So the point of the screw pushes the gib directly in, or with a slight anti clockwise twist, as opposed to it sliding on the slope of the gib strip and rotating the thing clockwise.

I guess i'll give it another shot tomorrow.

[chipenter]

You could drill through the slide and the gib and put dowels in , so the gib slides on the dowels and stops the gib twisting .

[S. Heslop]

You could drill through the slide and the gib and put dowels in , so the gib slides on the dowels and stops the gib twisting .

I'm still not sure if that would actually give full contact unless the dowels were very well aligned. I figure it'd be best to encourage the thing to get pressed flat against the dovetail while still floating. Shimming the gib or making a new gib that fits perfectly feels like it would be the same.

I wonder if filing flats into the gib where the screws contact would do anything. I might be totally wrong about the need get the screws to contact the gib perpendicularly to prevent it twisting though.

[vtsteam]

Steve, after now seeing the actual pictures of your gib strip, I agree with David and others, it's all wrong. The angles of the cross section MUST match the angles of the carriage and ways, (they don't). And the gib should extend the width of the carriage, top and bottom, for a sliding fit. It shouldn't be able to cock at an angle.

I also don't think is a big problem that it is fairly wide as long as the size and angles are right.

The dimple fo the screw should be "as if" you had run a drill through the gib screw hole with the gib in place to mark it. That's all you need. just a mark, not a hole. Something to just prevent the tip of the screw sliding along the gib face or allowing the gib to slide out lengthwise. Don't overdo it.

I say "as if" drilled through the screw holes because in fact that's what I did to make my lathe before cutting the gib screw threads. If I'd done that after the threads were cut, there's some danger of messing up the threads. It's still do-able if you're careful. Anyway, that gives you a mental picture of the orientation.

Yes you can make a new gib from strip stock with a file Steve. It really won't take long, and you only have to do it once.

Make yourself some filing guides out of some hardwood, ripped to the proper angle, and clamp the strip between them in a vice and start filing with a good clean file. A  reasonably fine tooth file file won't file the hardwood  much, so they will work.

You should mark out the gib beforehand with magic marker (blue it) and a scriber. All around -- both sides. And remove the gib from your filing jig and check your progress to the lines every once in awhile. You will get there. If you do feel you've got too much wear on the hardwood,  second pair of filing guides are five minutes work -- in fact just rip out a long length of the stuff to have spares to begin with.

You're not making a precision fit by the way, the bearing face isn't the one you are filing -- you just want to have a good fit in the carriage so the gib won't cock. I'm sure you can do it without a milling machine, having seen your helmet and other quality work. I'm very confident you can make your machine work to your satisfaction, even if you plan to sell it some day. And you will have a lot of satisfaction making something better than it was new. By dong it right.

[awemawson]

Once in Steves jig you could remove the majority of the material with an angle grinder then finish it with the file.

[PekkaNF]

First, interesting picture:
http://lh5.ggpht.com/_ozT1G3WqXg4/TUqsPuzQqeI/AAAAAAAALKM/HweM0rgDKQU/s800/gib.jpg

I think it is very hard to make this work this gib work with set screws. As mentioned before this gib is rhobic and tends to tilt. Slender one is only marginally better but can be made to work.

Good news is that there is lot of space to make this correct old fashioned real tapered gib. You don't have a milling machine, that would make it easier, but I think it is possible to make pair with file.

I never liked the "lapping" method here. The first thing that most people of the lapping society don't get that this is a method that avarages and distributes error, but does nothing (or random) to align parts. Therefore it would require first corrective measures before averaging. Therefore lapping is not an alternative to scraping or such. Another misconseption is that you can easily "wash" grit/paste away and it's all done. I suggest a little further reading on industrial methods (from 1940 on....) and it all should come clear. I think that root cause of this problem is that after internet lapping it looks good and feels good and this is enough. Some turning experiments are done and usually no matter you do if you work hard endcome is satisfying......


Pekka

[Pete.]

That is the big problem with lapping - it's uncontrolled.

I checked all my stuff that has straight gibs and every single gib is full height of the dovetail. I think if you  cure this you'll get far more satisfactory results. If you were near me I would invite you to bring it round and we'd get it better than new I'm sure.

Loply I thought you would be interested in the upcoming scraping classes in Norway and Sweden?

[Arbalist]

I think he problem is that they have milled the slide with a huge gap and used a huge gib to fill it. It should be a lot more tall than it is thick and yet yours seems to be about square in that respect.
Not sure how I'd go about fixing that. One way would be to make a shim to glue on top of the gib to stop it lifting. Another would be to clamp the gib into the dovetail where it lives then drill through the screw holes to about 2/3 depth and make some dog point adjuster screws.

Agreed. They've machined it all wrong IMO. Most gibs I've seen are twice as high as they are thick.

[loply]

That is the big problem with lapping - it's uncontrolled.

I checked all my stuff that has straight gibs and every single gib is full height of the dovetail. I think if you  cure this you'll get far more satisfactory results. If you were near me I would invite you to bring it round and we'd get it better than new I'm sure.

Loply I thought you would be interested in the upcoming scraping classes in Norway and Sweden?

I would certainly be interested, would probably struggle to get time off work mind. I do love scraping and it's great to be able to align things absolutely perfectly - I made a master square a while ago and got it within 2 microns of 90 degrees! - I just think for a mini lathe it might be a bit over the top - usually all it needs is to be made to a tighter fit in order to allow less chatter - rather than made to perfect alignment.

Besides which, lapping the compound slide and cross slide ways/gibs is very unlikely to produce any negative misalignment (unless you go mad with it). The most important thing is to align the headstock, which I would probably be inclined to scrape.

The trick with lapping is you have the use your senses... You can grind some parts more than others, twist it a bit as you go to focus on the front or rear of the slide, etc. It's a skill in itself, much like scraping. It won't get you a perfect result but it can definitely improve a cheaply made machine, markedly, in a fraction of the time it would take to scrape it.

Reconditioning is not neccesserily limited to just scraping.

Case in point - I bought a 36" camelback straight edge from a machine tool reconditioning business up here in the north - the bloke had been doing it for 20 years and told me that if a machine is far out he will start with an angle grinder and a flexible disc... He said sometimes clients were shocked but he would get it to within a thou like that, then switch to the Biax.

[S. Heslop]

Well thinking that i'd probably have to make a new gib strip as was suggested, I figured I may as well go all out butchering the current one.

I tried my idea of filing flats into it.


And it worked, kind of. The bottom of the gib is now sitting flat (as in, the gib isnt trying to tip over like before) except that now makes it way more obvious that the gib angles really are off, with the dovetail being more acute than the gib itself.


It was awkward holding it down to file that face more acute, I had to do it half at a time.


And the gib now presses against the side of the dovetail. I'm assuming (and hoping!) that it isn't important for the dovetail to also contact the bottom, since I did overdo the filed angle a bit.


I was having a hard time then getting the screws to feel right, so I took the gib out and used some of the engineers blue (it really does get everywhere!) and the lathe bed ways to check how flat it is.


I might try scraping it flat, since I'd also checked the bottom of the saddle and it wasn't contacting along it's full length, so it might give me some scraping practice before I start trying to adjust something harder to replace.

For now i'm taking a break because it is HOT today!

Thanks for the help so far though. Thinking about it, people were telling me that the angles were off but I just didn't think that the gib would be wider than the V it's trying to go into until I saw it myself.

[RotarySMP]

I feel your pain. I had a Sieg 7x  as my only machine for nearly 10 years, and modded it extensively. At the end of the day it is a lot of work to improve the 7x, and you still end up with a machine with a number of severe design deficiencies such as short sliding, bearing surfaces. My advice is to move up to a quality lathe as soon as possible, as any time spent improving an old worn quality lathe will at least be rewarded.

[Pete.]

Besides which, lapping the compound slide and cross slide ways/gibs is very unlikely to produce any negative misalignment (unless you go mad with it). The most important thing is to align the headstock, which I would probably be inclined to scrape.

The trick with lapping is you have the use your senses... You can grind some parts more than others, twist it a bit as you go to focus on the front or rear of the slide, etc. It's a skill in itself, much like scraping. It won't get you a perfect result but it can definitely improve a cheaply made machine, markedly, in a fraction of the time it would take to scrape it.

Reconditioning is not neccesserily limited to just scraping.

You could certainly improve the fit-up of parts as far as increasing bearing surface goes but even that has some negative aspects. Lapping will bring the faces to very close contact causing slip-stick as well as accelerating wear. Another thing to consider is that anyone who is looking for advice and wondering if lapping is an effective solution is unlikely to know when they are causing good and when they are causing harm (though I still say that the whole idea is a bad one). Thy could easily end up with a worse machine than they started with.

[S. Heslop]

Another thing to consider is that anyone who is looking for advice and wondering if lapping is an effective solution is unlikely to know when they are causing good and when they are causing harm (though I still say that the whole idea is a bad one). Thy could easily end up with a worse machine than they started with.

Yeah i've definitely felt/ worried about this.

I've also felt that i'd probably be getting a bigger lathe at some point since the mini lathe is often too small to do alot of the stuff I'd want to do with it. It's definitely handy and I don't ever regret buying it, but it's put me off wanting to put too much effort into adjusting or modding it. I'm only doing it now because I need better accuracy for this electric bike.


Anyways, I bent and filed that gib strip flat enough (contacting at 3 points. It bent more right in the middle because of the chunks i'd filed out), and then spent a while scraping the under side of the saddle. It now contacts most of the way across, and assuming I haven't made a huge mistake with the alignment, it should be an improvement.

Now I just need to shim the saddle gibs. I bought some shim stock assortment from amazon and really didn't get much in the package, but it should be enough for this I hope.

Oh also it turns out the compound slide has the same problem as the crossslide had. I don't think i'll bother fixing that since I usually just tighten that gib down till the compound can't move. The compound dovetail is milled out of parallel (I think) so it's useless for turning a serious taper. I've been tempted to replace it with a solid block of metal like people do on CNC conversions for rigidity, but even rough tapers are useful sometimes.

[Pete.]

My T&C grinder came with a whopping 20 thou taper in the ways, from wear rather than from poor manufacturing. I've got rid of that so anything is possible.