Gibs, adjustment screws and brass

[Tom S.Participant @toms]

Hello all,

Having purchased a mini lathe of Theseus from China, I decided to get started by replacing the original gib strips (top and cross slide). As Arceurotrade had a fairly handy set available for under 20 quid, this leads to my perhaps beginner question (and hopefully not an unholy war on correct adjustment! &nbsp.

The instructions with said kit are fairly straightforward, but suggest that the conical tip screws should be used to form a dimple in the brass by tightening (once the brass strips are in the correct place). This seems a little odd to me, but as I'm a beginner, I thought it'd be worthwhile to get other's opinions.

In particular, watching Dave M's channel on YouTube, he was talking about how the original mini lathe strips don't allow any sideways movement (with the original screws, there's just three drilled holes in the original gib), and to fix this via filing a concave cutout in the opposite side and flipping the gib (or similar methods).

Do we want the gib strip held in a specific location (i.e. via the indenting approach with conical screws), or is this a poor approach?

The kit's gib surfaces that face the dovetails are also rather rough, instead of smooth (machining mark pattern, but easy to feel with a fingernail and causes a dti to vibrate around a few thousandths). Should this be smoothed, or left for oil retention?

And lastly (phew!), I've also read that gibs should be slightly high in the centre (facing the interior of the dovetail) – unfortunately, these strips are low on one end only (by about 1/1000th). I could work on wet/dry on a surface plate to get them flat, unless there's a better reason to get them high in the centre? If so, by how much?

And there's probably going to be many opinions on this one – apologies for the length of post. I'd rather take the right approach before shaving metal bits off!

Many thanks

[Tom S.Participant @toms]

[SillyOldDufferModerator @sillyoldduffer]

Um, not come across Dave M before; I think this is the YouTube advice you mean Tom. (Dave M gets to the mini-lathe towards the end of the video.)

A general concern is that Dave has an immaculate workshop. Nothing wrong with that except it can be a hobby in itself, which isn't for everybody! Personally I'm more impressed by visible signs of work.

Anyway Dave's top 10 mods (with slight confusion in the telling) were:

1. Smooth operation of the compound (Tom's starting point)
2. Vibration
3. Quick-change toolpost
4. 3/8" set of carbide insert tool-holders
5. TCMT for aluminium
6. A work-light
7. Collets
8. Tailstock adjustment (apparently everyone else does it wrong)
9. I heard Spine Drills, I think he means 'use spotting drills rather than centre drills to start a hole'
10. Good boring bars

I'd agree with 1,2 and making sure the tail-stock is aligned, also a well lit workshop is a good thing. The rest of the top 10 are much more dubious, and I wouldn't take them too seriously.

In the case of the compound Dave M mentions a friend pointing out it was loose. This is a bad thing, but fixing it is an adjusment. Thereafter, it may be possible to improve smoothness by polishing the gibs, and some llike to switch to brass gibs. Whether any of it is necessary depends on the lathe. Early Chinese lathes came in for a lot of stick for poor finish; recent ones seem a lot better.

When I a new minilathe owner, I too read on the web that gib polishing would be an improvement. Some said it was essential, others that it was highly worthwhile. So, even though the lathe worked OK I stripped her down, agreed the gibs looked a little rough, and polished them up. As far as I could tell the effort was a complete waste of time – as the lathe was OK before, any improvement was miniscule. Lesson learned: if it ain't bust, don't fix it!

Now my advice to beginners with a new machine is to use it comprehensively for at least a month before jumping to any conclusions. Drill holes, face off, turn, thread and taper. Find out about tool profiles, depth of cut, feed rates and different materials. Gross faults apart, in the early stages disappointing results are as likely to be down to the operator as they are to a maladjusted machine. It's quite easy to confuse yourself and proceed unwisely.

Once you've given yourself and the machine a thorough test drive, it's much easier to diagnose faults with yourself or the machine, ask for advice, and then to fix it.

To answer the indent question, as far as I know fitting the cones into dimples is common practice. You don't want the gibs moving on their own. The ArcEuro method uses the lathe as a template to put the dimples in the right place; it's just an easy way to line them up.

Neil Wyatt of this forum has published a book on the mini-lathe. I feel it's more trustworthy than some YouTube advice, and you can always ask the author a direct question on here.

Dave

[Tom S.Participant @toms]

Many thanks for the advise Dave – I have a copy of the David Fenner books, but not Neil's. Looks like a nice book to grab.

I have adjusted the default gibs (although it's hard to tell exactly how tight to get them. One thing I've noticed there is that the gibs tilt, rather than staying with their inclined faces parallel to the dovetails, which also seems off. I'd expect them to be entirely parallel. (I'm also getting chattering/poor surface finish).

I'll go ahead with the 'ram the set screw into the gib' approach and have a read of that book!

Tom

[Neil WyattModerator @neilwyatt]

Hi Tom,

Misaligned dimples can be allowed for by filing grooves, but the Arc approach should ensure they are in the right place in the first place.

Counsel of perfection (from GH Thomas) is to put a dowel through to stop any gib movement, I haven't found the need to do anything more than adjust them carefully (and I may have also filled/scraped off the sharp edge that sits in the corner of the dovetail).

A ground surface can sometimes look rougher than it actually is but if the actual surface is accurately flat they can help by holding oil. The two times I've made a gib strip with mirror finished hard brass it's run smoother after being carefully matted with emery paper.

Neil

[Clive FosterParticipant @clivefoster55965]

The dowel to stop gib movement is a very desirable feature not mere counsel of perfection. Something I always add on a refurb along with proper conical holes for the adjusters to seat into. Preferably ball ended rather than pointed screws but allegedly a cup end and a ball bearing is as effective.

Gibs do tend to try and slide back and forth as the direction of slide movement is changed. Eventually plain dimples get distorted which makes it hard to adjust things just so. Especially after Harry the Hamfisted gets in on the act and over tightens the screws distorting the points as well as ripping up the dimples. Few years and iterations of that and no chance of a nice adjustment. On Boxford, Littlejohn and Southend size machines re-working gibs, pinning and using dome ended screws generally restores performance to at least new so long as wear is not silly excessive. I'd guess operating clearances can be got down to around half of standard.

Messrs Smart & Brown used conventional gib strips with two locating dowels on my 1024 apparently considering it better than the more common, and cheaper, taper gib. I'm not going to disagree. When you are selling a 5" centre height lathe at an ex-factory price comparable to that of a more than acceptable house the customer is entitled to expect things to be really right.

Clive.

[Pete RimmerParticipant @peterimmer30576]

Posted by SillyOldDuffer on 04/10/2018 14:23:59:

Um, not come across Dave M before; I think this is the YouTube advice you mean Tom. (Dave M gets to the mini-lathe towards the end of the video.)

A general concern is that Dave has an immaculate workshop. Nothing wrong with that except it can be a hobby in itself, which isn't for everybody! Personally I'm more impressed by visible signs of work.

Dave

You certainly shouldn't judge a person for having an immaculate workshop. Most of us would kill for this guy's setup and his work is incredible. On top of that Edvind's just the nicest guy and supremely modest. I spent the week with him on a hand-scraping course.

http://www.missiseipi.com/

[Peter G. ShawParticipant @peterg-shaw75338]

The gibs on my milling machine were knife & fork affairs. Plus the table was bowed. The table was reground, and I had to make new gibs. From information found around, here's what I did:

Scrape the new gibs to fit in the dovetails.

Fit a permanent dowel pin in the Y slide, and for the X slide (which needs to be removable) I used a removable pin made from a screw.

Fitted two extra adjustment locations on the X slide & one on the Y slide (size prevented any more).

Fitted 4mm ball bearings between the adjustment screws and a drilled location on the gib. To do this, I made a temporary adjustment screw with a 4mm hole down the middle. Then, with the dowel pins inserted to locate the gib, drilled a V shaped dimple equivalent to the bevels on the front of the 4mm drill (hope that makes sense). The ball bearings now sit in the dimples, which by virtue of being drilled in situ, are now correctly located. The balls are held in place by the adjustment screws.

Does it work? Don't know because I'm very slowly, extremely slowly some might say, incorporating as many mods to the machine as I can do, and at the moment it's in an unusable state awaiting the latest mod completion followed by tramming etc. What I can say though, is that all the info I found suggests that it should indeed be better.

By the way, I used steel for my gibs. I've a sneaky suspicion that one of the articles I found said that brass probably wouldn't help that much if all the other stuff was done.

Peter G. Shaw

[SillyOldDufferModerator @sillyoldduffer]

Posted by Pete Rimmer on 04/10/2018 19:37:40:

Posted by SillyOldDuffer on 04/10/2018 14:23:59:

Um, not come across Dave M before; I think this is the YouTube advice you mean Tom. (Dave M gets to the mini-lathe towards the end of the video.)

A general concern is that Dave has an immaculate workshop. Nothing wrong with that except it can be a hobby in itself, which isn't for everybody! Personally I'm more impressed by visible signs of work.

Dave

You certainly shouldn't judge a person for having an immaculate workshop. Most of us would kill for this guy's setup and his work is incredible. On top of that Edvind's just the nicest guy and supremely modest. I spent the week with him on a hand-scraping course.

http://www.missiseipi.com/

Thanks for that Pete – nothing beats a personal recommendation!

I guess I'm overly suspicious of immaculate workshops because mine is a pigsty. Some of my work is incredible too – just not in a good way…

Dave

[Tom S.Participant @toms]

These gibs (and indeed, the original compound are… well, definitely not ground). Try not to shriek, but here's a gallery of the gibs, plus bonus shots of the compound. (I ordered a new casting from Arc, which is much, much better than random lathe seller).

**LINK**

I've fitted them as is for now, and having taken the compound apart, I feel the urge to improve how the dials/handle assembly works…

I've gone with the gibs as is for now, but it may be worth sanding them down a touch…

Tom

[Pete RimmerParticipant @peterimmer30576]

Perversely even though the fly-cut surface looks rough if it's flat then it will work (for a short time) better than a totally smooth way. The trouble is that bare machined surfaces are usually not close to good enough to make for a good way bearing. I don't think I have ever blued up a cross slide or compound and got what I would call a workable bearing right from the off. Some have been very good but the vast majority have had less than 10% of blue transfer onto the surface.

Also I don't like brass as a material for a gib. I'm guessing that the gibs they sell are brass because they are easily produced and people associate the brass with bearing bronze. Brass is usually very soft so embeds particles easily and when whatever lube is on it dries out it gets quite 'gummy' in it's sliding behaviour. Cast iron and steel are much better, I've made several from gauge plate which I think is my preferred material for a flat gib..

[John Hall 7Participant @johnhall7]

I have a Warco 250v-f and have found the top slide gib is both quite thin between the dovetail, and also quite short top to bottom.. it therefore  has the same problem as mentioned earlier, of tilting when the adjustment screws are tightened…This sloppiness has also caused the indents on the gib not to be drilled parallel with the edges, they line up diagonally along the length of the gib…explaining why I had problems adjusting it

the cross slide gib is absolutely fine, and is a good fit sideways and up and down, and doesn’t have the tilting problem..

im going to make a new gib for the top slide out of thicker wider brass…hopefully that should cure the problem…

PS…anyone buying a new..or old Warco…I would suggest you remove the gearbox and apron assembly and give them a thorough clean out with white spirits…mine had way to much cast iron grit in the bottom..

im also thinking of fitting an extra drain plug in the bottom of the gearbox as the one on the side is obviously higher than the bottom of the box, meaning it doesn’t drain fully…magnets are also being fitted in the plugs for good measure.

stay safe…

Edited By John Hall 7 on 09/05/2020 17:25:29

Edited By John Hall 7 on 09/05/2020 17:26:03

Edited By John Hall 7 on 09/05/2020 17:26:51

Edited By John Hall 7 on 09/05/2020 17:27:42

Edited By John Hall 7 on 09/05/2020 17:28:25

[Jouke van der VeenParticipant @joukevanderveen72935]

I recently made a gib strip from brass for my Emco Compact 5. Dimensions were chosen the same as originally supplied by Emco but I made it a bit longer. I polished the sliding surface on fine emery paper P400.

It was positioned such that the top edge touches the cross slide along the total length. And, of course, the bottom side is completely free from the saddle. With the gib strip clamped in this position I dimpled the strip with a pointed pin through the three gib screw holes.

And I must say: movement of the cross slide with this gib strip is as it should be.

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