Sieg SC3 Mini Lathe - Let the adventures begin

In the last few weeks I have sold my Unimat 3 and moved to a slightly bigger lathe in the form of a DRO fitted Sieg SX3. For those not familiar with machine speak DRO stand for digital read out.

Chris and I travelled down country to Newark yesterday to collect it and because it's quite heavy I had to strip it down to be able to lift it into the house between us. So today was spent reassembling the compound slide and refitting the chuck.

Looking at YouTube there are many modifications to improve the small Sieg and other types of mini lathes sold under different brand names - Apparently there are at least three different Chinese factories building lathes to the same basic design but have different bed lengths, motor sizes/types etc. The biggest difference seems to be that most are built to the C3 design which has a brushed motor and two gear ranges.

The Sc3 has a more powerful brushless motor with direct drive allowing 0-2500 rpm spindle speeds without needing to manually change gears. The minor drawback with my machine is that it's imperial whereas I am much more familiar with the metric system but that should prove too much of an issue because the DRO's can be set to Metric taking out most day to day need for conversion. The time when it being imperial will affect me is if I do any screw cutting because all the gears are imperial and I am not certain at the minute if I can cut metric threads or not.



This is it so let the fun begin.

 

Do feel free to contribute your efforts as you get into it. It can become quite addictive.
It's odd that although I had nothing specific to make after sending the Unimat to you and waiting to arrange collection of the new one. I felt like I was missing a limb or something. Very strange.

 

Funnily enough I had watched a couple of videos on doing that very thing and if this one hadn't come up that may well have been the next mod on the Unimat.

 

Prior to Christmas I had decided that the week between Crimbo and the New Year I would spend ironing out the wrinkles with the new lathe.

First I stripped down, cleaned and deburred all my chucks.

The lathe came with two 3 jaw chucks (80mm and 100mm) and a 4 jaw chuck.
I have seen a few reviews on YouTube of Chinese import chucks and it seems that although basically sound bits of kit, to keep the price down they don't do any cleaning or deburring post machining which means that many of them have all the grinding dust present inside which if mot cleaned out will drastically reduce the life of the chuck.

The 4 jaw chuck cannot have been used because when I tried it before stripping it down to clean one of the jaws wouldn't actually close due to burrs in the slides. I also took the opportunity to strip down and clean another 3 jaw 80mm chuck that I had bought in October with my rotary table for the mill. The latter is actually the best manufactured of all of them needing very little to getting running smoothly.
Next up was the ball handle for the compound/top slide. I didn't take a photo of it prior to starting work on it but it should look like the one on the left (from the cross slide)

I am not sure if the handle had been broken off at some point or just crudely sawn off but I wanted to replace the handle part. I am pretty sure that I could probably buy a spare from Amadeal but where is the fun in that.
So I made a fixture out of an M10 cap screw a couple of nuts and some washers to hold it securely in the milling vice and drilled it almost to the bottom. I did consider that I might have to drill it right through because I didn't think that I had an M6 plug tap but I found one in a drawer so I was able to retain the chromed ball. The plan is to make a handle similar to the other one from stainless steel rod once I get the lathe back together.

 

Prior to buying the lathe I did quite a bit of research and one of the things that I picked up was that in being made to a price, these Chinese mini lathes lack the rigidity of their bigger higher end 'professional' cousins. What quickly became apparent though was that they can be made much more rigid for the outlay of some time and very little money.

What the Unimat had but the Sieg hasn't, are the means to lock the carriage, cross slide and compound slides. I have already attended to the latter two by drilling and tapping more M4 holes along the Gib strips.

I did the compound slide first, you can see the new holes by the remains of the marker pen that I used for marking out.







Then the cross slide, I didn't need as many additional screws on this one as it was already supported towards the end of the Gibs


Two screws on each slide wont have lock nuts on them and they will act as the locks when tightened the rest will have grub screws and locking half nuts to position the Gibs to allow smooth travel of the slides.

 

If you think that's brave, wait until you see what's coming next...

 

When I picked up the new lathe and gave it the once over I noted that there had been some upgrades carried out already which rather surprised me that whoever had done it hadn't fitted a carriage lock etc.
One of the other recommended improvements that people make is to fit a swarf guard to the back of the apron (for those that don't know what an apron is and I didn't it's the gear housing for the carriage hand wheel which also houses the auto feed mechanism). Most people that I have seen make such a cover have done it from thin perspex sheet which works fine but I was delighted when I saw that mine had a brass cover.



I was even more delighted when I took it to bits and found out just how well it had been made. You will also note the grease nipple. Grease nipples have been fitted to all the bearing housings.

 

Now onto a scarier upgrade.
This is the bottom of the main carriage.




The two black strips that you can see screwed to the underneath of the carriage are hardened steel and they stop the carriage from lifting. As you can imagine the needs to be a bit of clearance between these strips and the underside of the carriage to allow it to slide along the bed of the lathe. As delivered this clearance is adjusted and fine tuned by the set screws and locking nuts that you can see between the cap screws. As I understand it these lead to cracking of the hardened plates over time.

I have seen a few ways to over come this but the best way that I have seen is to remove these grub screws and replace them with an appropriate thickness of brass shims. The person I saw who added shims just had lots of bits of shim balanced in between the two surfaces but a Gent in the US improved upon that by making a jig to drill out the shims to match the hole spacing of the main cap screws thus preventing them from being dislodged while being refitted to the lathe.

Next is to replace the cap screws with stainless studs and nyloc nuts and then remove one of the hardened strips and replacing it with a mild steel strip of more substantial proportions.



There are a couple more bit's of material that I am waiting for so the rest of the description will have to wait until then.

But in the meantime, the next job is to mill out the carriage where the blue blocks are to take the two pieces of square stock in the image these will be screwed to the ends of the carriage in the milled gaps and will form the anchors for the carriage stop.

 

As I mentioned elsewhere, I had a first go at Fly cutting with the mill last night.
The pieces of bar in the photo above are what's known as hot rolled steel. Hit rolled steel is the cheapest way to buy steel but you do get an outer coating of oxidisation and the edges are far from flat/square

For the two larger pieces I needed to square up the edges and then flatten one face. I had two options use an end mill or fly cut them. I used an end mill on the edges bt for the larger area it would have taken a fair amount of time to flatten it with my largest end mill with is 10mm. With a fly cutter I could do the whole area in one or two passes at each cutting depth.
The other thing that appeals to me about fly cutting is that it uses a piece of tool steel similar to a lathe tool and is something that I can confidently re-sharpen in the workshop on the grinder. I have no means of re-sharpening end mills so they become quite expensive consumables.

This is the fly cutter in action, it was spinning at 740 rpm and I was taking off 0.04mm per pass

 

Although I have been waiting for delivery of various bits of metal and fixings which have been trickling in over the last few days (I have everything I need now, I think or should that be hope). I haven't been idle.


I got the stainless steel lock nuts for tensioning the Gibs on the two slides and managed to get those ready to refit.










The last photos also show an anti backlash nut/block which I hope will take out the backlash from the cross slide lead screw. It's an idea I got from the US YouTuber that I mentioned (username of Dr Jim) who made his from oil impregnated bearing bronze. I looked into getting some and nearly had a heart attack so settled for testing the concept in acrylic as I had seen another person do who had fitted anti backlash blocks to a home made CNC Mill.


Whilst making the anti backlash nut/block was quite simple. Finding out the thread size/pitch was a bit of a challenge and I am grateful to members of the Model Engineer forum who between a few relies gave me the information that I needed to work it out.


Why was it so difficult you might ask. Well, I have previously mentioned that the machine is imperial but fitted with Digital Read Outs on the cross slide. From what I have read, when fitting the DRO kit's the lead screw is replaced as part of the upgrade. I rang Chronos who are the supplier of DRO kits in the UK who told me that the lead screws included in the kits are metric. On this basis it seemed logical that the cross slide leadscrew may in fact be metric.


As you might imagine a query on the ME forum elicited quite a few helpful answers and a few less than helpful ones thrown in for good measure. Ultimately I was pointed in the direct of a US site and advised that some of the machines actually came factory fitted with DRO's and they retained imperial lead screws. With the help of replies that were specific with information I finally worked out that my cross slide leadscrew is a left hand thread 3/8" 20TPI. Part of my difficulty was that I had no idea of how BSF threads were actually measured as I have never had cause to buy or measure any BSF fixings. All my experience has been in Metric or for modelling purposes, BA screws etc. Where we specify the whole thread length.


A set of taps was duly ordered from RDG engineering supplies (£10.96 inc. postage) and the job was done.

 

Next comes the most daunting part so far, machining the carriage casting to square up the cut outs in each side to take the extension pieces which will support the carriage stop.

Being a casting, the very nature of it is rounded corners and rough finish. At the very least the faces needed flattening to take the machined block which is to be let into each cut out. As I was studying the cut outs to determine how best to machine them, I noted that at the side where the inverted V was machined into the base there was a distinct slope to the edge of the cut out.



When I check this with a protractor it was almost 80 degrees. There wasn’t enough casting left to make this edge vertical without cutting into the inverted V so it made sense to machine this edge to 80 degrees. I reasoned that cutting the opposite edge to the same angle would also help relive any potential stresses on the M6 screws that I plan use to fasten these infill blocks to the carriage, when the lock is tightened down.



I then machined the ends of the infill blocks to suit the angled cut outs.






All this was made less stressful by the knowledge that a replacement carriage casting is only £23 plus P&P.

 

Ouch, that really does sound like hard work.

It was bad enough doing it by machine. Still I am getting there and the last piece of bar that I needed is cold rolled without the black coating so will be much easy to bash into shape.