Sieg C2 mini-lathe mods

[spuddevans]

So after too long a break from posting up anything, I've decided to chart my progress as I try and improve my little mini-lathe.

Let me introduce the patient.



It is a Sieg C2A mini-lathe, badged by Axminster (I doubt if that makes any difference) I bought it about 5 or 6 years ago (I think  ) and up to now the only mods I have made to/for it is to chisel off the majority of the anti-rust "dragon fat" and to install a QC toolpost.

I have been quite happy with the lathe, it has done most of what I wanted from it. However, parting anything harder than warm moist butter has always been a little "Buttock-Pucker" inducing. Also the carriage has always been a little stiff, and the gears are constantly jammed up with swarf. The topslide (compound  I'm useless with proper terms) DRO has stopped working and the action has always been so poor I have just kept the gibs fully tightened up to lock it solid.

So what's the plan? Here's the list in no order of importance.

Tapered gibs on the carriage,
Carriage lock
Replace gibs on cross-slide and topslide with brass gibs (or learn how to scrape the existing gibs to fit properly)
Build a replacement QC mounting block to replace the Top-slide (I don't use the Top-slide/compound except on rare occasions, when I will re-mount the top-slide)
Convert the tailstock to a cam-lock.
Maybe change the headstock bearings to Angular Contact.



So I've made a start on the 1st item, the Tapered gibs.

Because I have only one lathe I made a start by making the gib-adjustment screws (it's pretty hard to turn them when the lathe is in bits)

The screws are M4 threaded, with a 11mm diameter head. Rather than wastefully turning down a long section of 12mm brass, I decided to follow (of a fashion) C.Fellows and make it out of a socket cap screw. Not having any M4 cap screws I used the next best thing I had, a couple of M4 Pozi screws, and a couple of 12mm "washers" I turned up and tapped M4.




Then I fluxed them up and set them up to silver solder in my little hearth.




In the interests of honesty, only one actually "took", I think that the screws may have been Zinc plated, which caused one not to stick, funny as the other one seems fine. So I had to redo one, but this time I turned the end of the screw down to 3mm, then drilled another brass "washer" to fit and then silver soldered it.


Then I chucked them back into the lathe and cleaned up the faces and turned them down to 11mm.




Then it was over to the mill to mill a screwdriver slot.




Resulting with this,




Having a little more time before the call to dinner, I started on cleaning up the hunk-o-rust that will become the gib brackets.




That's as far as I got, stay tuned for (ir)regular updates.


Tim

[ttrikalin]

Good job thus far!
Nice documentation and good photos.

Thank you,

Tom

[Roger B]

I would definitely recommend fitting taper roller bearings to the headstock. There are a few potential problems and with only one lathe you need a bit of planning.

This was my experience:

http://www.modelenginemaker.com/index.php?topic=2866.0

[spuddevans]

Thanks guys

This was my experience:

http://www.modelenginemaker.com/index.php?topic=2866.0

That thread has been bookmarked, some great info on the tailstock mods, thanks for that


Nothing much to show for today, I just removed the rust and squared up 2 lumps of steel, and in the process flattened a section of my carbide lathe tool that I used in the flycutter. ( I'm glad I wasn't using a HSS bit, I'd have been sharpening it every half inch )

Next will be stripping down the lathe carriage to measure up exactly where the mounting holes should be installed, then it will be onto milling the taper into the brackets.


My playtime in the workshop was cut slightly short today as I had to go to the post office to pick up a little bundle of toys from Arc   

I got a new Digi-vern (one of the new orange screen ones, bought to replace my last 2 that had suicidal tendancies and threw themselves off the workbench, which somewhat negatively affected their accuracy/use) a set of Stevenson's ER32 blocks (what a great idea) and a ballrace ER32 nut, and a couple of small items.

So, onwards and, Umm........  sideways

Tim

[MMan]

Hi Tim,

I built a replacement QC mounting block for my C3 (same thing, just a bit longer). The problems with the QCTP on the compound I was trying to fix were: too much overhang towards the chuck and too much flex in the compound slide making parting and cutting hard material eventful and cutting larger diameter work like flywheels, with the compound skewed round, was kludgy and not rigid enough.

Basically it is a 50mm cube with the QC parts recessed into it (unlike the standard one where they stick out) which mounts on a 20mm plate with T slots which bolts to the original swivel plate in the cross slide. The T slots let you move the tool holder out for larger work or, because it rotates on the swivel plate, move the tool post forward and back (for skimming things that won't fit over the cross slide). The hold down bolts through the cube are on a square pattern so that the cube can be rotated in 90 degree increments for boring etc. It takes the original holders although I might make some improved ones when I get to it.

Doing this has made parting much easier and I now get a far better finish on harder materials like silver steel (drill rod).

Pics below.

Mman

[spuddevans]

Hi Mman, Thanks for those pics, that's the sort of thing I am thinking of.

I started today by reducing the brackets down to the dimensions I needed, 19mm x 15mm. I decided to leave them a little longer than the carriage width for an idea that will be explained later (or if the idea turns out to be rubbish it will be forgotten about  )

Then I dismantled part of the Carriage in order to be able to measure it up. For those who may be wondering what the underside of a mini-lathe carriage looks like, wonder no more...




And before you ask, yes it did come with one cap screw missing. Setting these gibs up requires the employment of an octopus in order to loosen 3 screws while tightening 1 or 2 others. Hence the attraction to upgrade to a "single screw" operated tapered gib.

After removing the original gibs I set about measuring up to transfer the holes to the new brackets. I first up measured the diameter of a M6 capscrew, and then halved the result. Then I set my digi-vern to this value and zeroed it. Then by measuring from a datum edge (I chose the edge that would normally be closest to the headstock) to the far side of a M6 cap screw in each of the holes like thus,




And by repeating the same procedure but using the front or back edge I was able to note on the plans exactly where the centre of each mounting hole should be installed. I guess in the factory they just drill these holes without any real reference as no two holes were aligned!!




So after measuring, noting, drilling and de-burring I ended up with this.




Next up will be cutting the tapers, Thanks for watching



Tim

[Roger B]

Just a quick note, make sure that your thicker gibs clear the drive gear. Mine had very little clearance.

[spuddevans]

Just a quick note, make sure that your thicker gibs clear the drive gear. Mine had very little clearance.

That's a very good point, I will re-assemble the carriage and check that tomorrow before cutting any tapers, it'll be easier adjusting it now while it's still square. Thanks for pointing that out 


Tim

[Danny M2Z]

G'day Tim.

Re: Parting off in a mini-lathe. Turning a parting tool upside down and mounting it in a QCTP, then running the mini-lathe in reverse gives a similar result as the people who use rear mounted toolposts on other lathes. It is perfectly safe btw, due to the mini-lathe having a bolted-on chuck.

Also I found a tip which entailed slipping a small ball bearing under the tip of the gib screws to improve things in that department. I'me not sure how or why it works, but it does.

Also, a carriage stop is invaluable, saves embarrassing crashes and is great for boring work. (There are a few designs online)

I found that angular contact bearings are available in the same physical dimensions (ARC Eurotrade) as the standard bearings, so one does not have to machine the spindle to fit them (as you do if tapered roller bearings are used.

I took my Seig dro's off btw, they are not accurate (backlash) and prevent one from swinging the top-slide around to 29.5° for screwcutting by the single flank method.

Once they receive a bit of tlc, it is surprising how well these little lathes can be fine tuned.

* Danny M *

[spuddevans]

Hi Danny,

I've heard of that tip about the parting, hopefully when I'm done parting will be easier, but I will keep that in mind just in case.

Thanks for the other tips too. That's why I was thinking of Angular contact bearings instead of taper bearings, less Lathe-ing without the use of a Lathe.

I like the cross-slide DRO, as long as you remember about backlash, I've found them very accurate. But it is annoying about their size getting in the way. I intend to replace the top-slide for most work with a solid post for my QC toolpost.



Anyway here's your warning!! Epic tome ahead.


I had the day off work today, so I got to spend much more time in the workshop. 

Before I start on cutting the tapers I wanted to cut out for the gear, as you can see it will not do as it is at the moment.




Also I tried the fit of the new gib brackets on the lathe and found that the front bracket fouls the rack by just a little.




So I took about 1.5mm off that bracket and then, after measuring the offending gear as being 17mm, I used a 16mm endmill ( the biggest I have ) and made the cutout.




And here it is in place.




Now that's done it was on to cutting the tapers. In Bog's thread about Darren's lathe he temporarily glued a 1.5mm pin on one edge to set the taper, and I was going to do the same when I discovered I didn't have any superglue. So I came up with an alternative version, and verified it using my little digi-angle-finder. I used a 1.3mm drill bit to space one end ( circled in red )




Then I rough milled it with a 3/8" roughing endmill and then finished it with a 10mm carbide cutter. Then I did the same on the other bracket, remembering to get the taper going the right way.





I was hoping to mill up the gibs themselves, but when I looked through my stash-of-scrap I didn't have any suitable pieces of brass. ( I did have some that was way too big, but the price of brass is too much to mill that much into swarf )


So instead I decided to press on with another little mod, the cover for the handwheel gears on the carriage. As supplied, it looks like this.




I was going to get all technical and start measuring up and marking datums, but then I realised that I could do it much simpler. I measured the shaft to be 17mm and, after cutting out a suitable piece of 1.5mm ali sheet, I bored a 17mm hole in what seemed to be roughly the right place. Then I had to file a little radius on one corner (red circle) so that I am able to manipulate it in and one edge fits nicely under the half-nuts.




Then, while holding the ali in place, I traced out the outline of the casting with a pencil. (actually I had to do this twice as I smudged it the 1st time )




Then I rough cut it on the bandsaw, remounted it on the casting and held it in the vice and carelessly filed it to shape, and then drilled the cover for mounting screws (and gently marked the casting too)




Then it was over to the mill to align by eye and then drill 2.5mm. I was only able to get one clamp on it so I took it really gentle when drilling. ( this casting drills and taps like a dream )




I seem to remember seeing someone else doing a similar mod and they found that the gears sit a tiny bit proud, and their solution was to mill a recess in the cover to prevent the gears from binding. My lazy streak kicked in and I thought I could make it a little simpler. Both gears have shoulders to space them out from the casting, and I measured the shoulders at just over 1mm.




Now if only I had a working lathe !!! But I do have a vertical lathe, of sorts.




As you saw, I even aligned the tool with the very same ruler I use to set the toolheight on my lathe. Actually I had to do this twice as the above tool was the wrong geometry.

It worked just fine, all I needed to take off was 0.25mm from each gear's shoulder.





Then after tapping the m3 holes in the casting I was able to mount the cover.




This what it looks like in situ





Sadly the brass I've ordered for the gibs wont be here until at least tuesday, so I will have to think up some other mods to be getting on with in the meantime.


Tune in next week to see what happens.

Tim

[Danny M2Z]

Sadly the brass I've ordered for the gibs wont be here until at least tuesday, so I will have to think up some other mods to be getting on with in the meantime.

While you have the mill set up, this might be a useful addition http://homepage3.nifty.com/amigos/stopper/stopper-e.htm

* Danny M *

[Roger B]

If the angular contact bearings are the same size as the standard bearings they will certainly be easier to fit (I suspect that just fitting good quality versions of the standard bearings is probably enough  ).

I have attached some notes on the taper roller bearings and also a link to the collet extractor I made as another possible mod.

http://www.modelenginemaker.com/index.php?topic=2089.0

[spuddevans]

While you have the mill set up, this might be a useful addition http://homepage3.nifty.com/amigos/stopper/stopper-e.htm

* Danny M *

That is a handy mod, I already have a depth stop that I bought, but it doesn't have the feature of using a dial indicator which could be handy

If the angular contact bearings are the same size as the standard bearings they will certainly be easier to fit (I suspect that just fitting good quality versions of the standard bearings is probably enough  ).

You're probably right about fitting good quality bearings, but when I do it I probably will fit the AC bearings as it seems they are a worthwhile upgrade.


Tim

[bp]

I'm planning on a similar series of upgrades for my Sieg C3.  I was wondering which bearings to fit, so I had a look in my SKF book and found the following in the Basic load ratings columns

Deep Groove ball bearing 30 x 62 x 16 - Dynamic load rating 19500N; Static load rating 11200N
Angular Contact ball bearing 30 x 62 x 16 - Dynamic load rating 23800N; Static load rating 15600N
Taper roller bearing 30 x 62 x 17.25 - Dynamic load rating 40200N; Static load rating 44000N

I knew that this would be the general trend, but I didn't realise that the difference would be so great.  For my money there's no doubt that my new bearings will be taper rollers, even though they are not a simple swap.
cheers
Bill

[spuddevans]

Deep Groove ball bearing 30 x 62 x 16 - Dynamic load rating 19500N; Static load rating 11200N
Angular Contact ball bearing 30 x 62 x 16 - Dynamic load rating 23800N; Static load rating 15600N
Taper roller bearing 30 x 62 x 17.25 - Dynamic load rating 40200N; Static load rating 44000N

Interesting figures  Quite a difference between them all.

I'll have to consider whether going to the extra effort of fitting the taper bearings over fitting the AC bearings. A bit more research needed me thinks.

Thanks for posting those figures.

Tim