Category Archives: Workshop Machines

Machines for making things, like other machines.

Spindle bearing replacement

March 2017

Paying some attention to the spindle bearings came about after a very good friend (and also my inspiration for all this machining malarkey) needed a simple alignment tool to aid assembly of a powered bifold door. I was keen to show off the engineering skills I had collected, however the 90mm-long piece came out tapered…

Before messing with the screws clamping the way to the head, I decided to at least have a look at the bearings.

The existing bearings in the lathe were marked with ‘Poland’ and ‘USSR’, so I think they were the originals (from the lathe’s manufacture in 1989). I could see very little sign of wear in the bearings, so I could have just cleaned / re-greased and re-installed them rather than installing new ones.

The shim washers however were in less good shape. The front one was clearly dished, and the rear one was a bit wavy, rather than flat.

Pulling the spindle is not a difficult or time-consuming job. Details of part numbers & sizes for the bearings and shim washers are below.

When I figure out how to adjust the bearings for pre-load, then I will add details in a separate page…

C-spanners

The spindle assembly is held in place by two collars: one to apply pre-load to the bearings, and the second one as a locking nut.

The holes in the collars are 4.5mm diameter, about 2 to 3mm deep. The collars are about 32mm in diameter.

I made up a pair of c-spanners by turning the rounded part (32mm ID x 50mm OD x 10mm deep), then adding a reamed 5mm hole for the pin. I then added a flat where the handle would be brazed on, and cut the round into two pieces (to make the two c-spanners).

I made the pins out of 6mm silver steel. I turned a 4.5mm diameter section to fit the collars, then a 5mm section to fit the reamed hole in the spanner, and finally I left the last 1mm at 6mm diameter. I did not harden the pin. I glued it into the spanner body using Loctite 603.

The handles are rather heavy for this application, but they were what I had in stock. I rounded the corners slightly to make them more comfortable to use.

My brazing skills need some work… I didn’t bother to tidy them up too much.

Spindle removal

Removing the spindle is straightforward, and is described in the manual. I have reproduced the instructions and exploded diagram below.

My lathe did not come with the part labelled number 4.

With the locking collars removed, ready to tap the spindle out. It is not necessary to remove the chuck back plate – in fact in the manual they advise against it due to the risk of misalignment on assembly. Because I was trying to fix a known problem with my lathe, I took it off (if you just want to check/replace the bearings, then don’t take it off).

You can see the bearing poking out. I was surprised to see that there is no seal to prevent ingress of swarf. When re-assembling, I’d suggest to go heavy on the grease to make sure a lip of grease surrounds the bearing, to catch any swarf. Having said that, the bearings were not worn and looked original (1989 vintage).

Spindle and front bearing as removed with a couple of light taps with a copper-faced hammer. The rear bearing is a sliding fit onto the shaft. The front bearing (in the pic) is pressed onto the shaft. I got it off the shaft by tapping around the edge of the bearing with a suitable punch/drift. To replace the bearing I used the old bearing shell to tap it back into place.

The bearing shells are a close sliding fit in the bore. They are supported on the inside by a circlip (visible in the pic above) and a 1mm shim washer.

The bearings were in great condition, with barely any sign of wear. Pretty good going for 30-year old bearings.

The 1mm shim washers were in less good condition. The rear one was wavy, while the front one was clearly dished (very difficult to get a photo, have done my best above of the dished front washer).

Bearing and shim markings and specifications

  • Front:
    • Markings: “USSR”, “7506”, some Cyrillic text
    • Size: OD 62mm, ID 30mm, width 21.25mm (assembled)
    • Standard bearing: 32206
    • SKF part number: 32206J2Q
  • Rear:
    • Markings: “Poland”, “30305A”, “FLT-8”
    • Size: OD 62mm, ID 25mm, width 18.3mm (assembled)
    • Standard bearing: 30305
    • SKF part number: 30305J2

I bought SKF brand bearings from simplybearings.co.uk. Part numbers are above.

The spacers are 62mm x 50mm x 1mm shim washers. I got mine from www.thebearingcompany.co.uk. They are also available on eBay but I was not convinced as to the quality.

I used Castrol LM Grease to grease the bearings.

Refitting

As the manual says, refitting is a reverse of removal steps. I tapped the front bearing back on to the shaft using the old bearing shell and a drift/punch.

I took great care to clean out the circlip grooves as these are critical to alignment.

I also used some Loctite 641 (medium strength) to positively locate the bearing shells inside the lathe head. This has a 20 minute cure time, so you should have plenty of time to get the spindle back in, tighten the collars and get the lathe running.

I tightened the collar by holding the chuck backplate in one hand and the c-spanner in the other. I got it as tight as I could, then ran the lathe of 15 minutes, then re-tightened. I would like to use a more scientific method, however torque settings for these bearings are application-specific, and the manual is unhelpful in this area…

 

Leadscrew thrust bearings

December 2014

One of the first things I noticed during the lathe rebuild was the lack of thrust bearings on the cross-slide and carriage leadscrews.

The standard arrangement features same-metal to same-metal ‘bearings’ lubricated by light oil dripped into the oil holes on the handle bosses. The key principle of plain (non-roller) bearings is that they are made of a different material to the surface being borne. The stock design doesn’t include functional plain bearings.

Carriage leadscrew

When I first started using the lathe, I thought that something was wrong when I tried to reposition the carriage, as the handle required so much effort to move. After oiling everything, and checking the tightness of the carriage on the way, I concluded that this is just how it is. Some googleing confirmed this as other people had the same problem with the MD65.

A quick search on eBay and a thrust bearing was on the way in the post. I took off the handle and fitted the bearing – the difference was significant, the leadscrew is now much easier to turn.

brearing

The bearing I used: AXK1226. To install it, undo the locking nut and unscrew the leadscrew handle, which should have the indicator dial attached. Insert the bearing onto the shaft and reverse the process. You apply tension to the assembly by tightening the leadscrew handle.

bearing installed

The arrangement of using the ally handle to apply tension is not good – in fact after installing the bearing I noticed that the handle was not square to the leadscrew, which explained why it was hard to turn at certain points in its rotation.

As with many such temporary measures, it became permanent. I ended up simply adding some large o-rings in the gap around the bearing (that you can see in the pic above), to protect the bearing from swarf.

A better arrangement would be to either bore a recess into the boss for the bearing, or make a ‘cup’. See the section below on the cross-slide leadscrew.

Cross-slide leadscrew

After using the lathe for a few projects, I felt that the cross-slide could also do with a thrust bearing. This would make adjusting the gibs easier and improve the feel of the lathe (as the resistance from the leadscrew would be removed).

I did a better job of this than the carriage leadscrew… The bearings are 4mm thick with both washers, I bored recesses for the bearings into each side of the handwheel boss. 4.0mm deep on the cross-slide side, and 3.8mm deep on the handwheel side – so that the handwheel butts up against the bearing. A little light oil on the bearings and you’re good to go.

The bearings are AXK08021.

CAD drawing showing the bearings as installed. What you can’t see is the shoulder on the leadscrew butting up against the far side of the right-hand thrust bearing. Tightening the handwheel clamps the two bearings around the handwheel boss.

As machined…

After installing the bearings, I immediately had to tighten up the gibs as the weight of the handle was turning the wheel and moving the cross-slide! This mod will improve rigidity as I can now adjust the gibs correctly, without getting false ‘tightness’ feedback from the handwheel.

 

Norman Patent Toolpost

November 2016

While I do love my little lathe, the design could do with improvement in a couple of areas… in particular the topslide (compound slide) which often fouls the tailstock, does not help with rigidity (even when locked), and adjusting it is a pain due to the four mounting screws and limited rotation.

The toolpost described below will hold tools of up to 1/2 inch, and is very rigid. The toolholders themselves can be easily adapted to many specialised tasks, such as a dedicated boring or parting toolholders.

The complete plans are here.

Options options…

I looked at many options, including a QCTP from the likes of Arceurotrade (who have a very nice little QCTP that is perfectly sized for the MD65/SD300).

Also my lathe came with a nice little low QCTP, which I considered re-purposing however it features two holes for mounting, which would make it difficult to make a mount that allows it to rotate.

However the problem with most of these options is that they are unsuited to the design of the MD65/SD300, which has a very small distance between the top of the cross-slide and the spindle axis (65mm). For most commercially available toolposts this presents a challenge: either they are just too tall or mounting them onto the cross-slide would be difficult (or both).

Lastly, a QCPT would not help with one of the key design requirements: rigidity.

Norman Patent Toolpost

Enter the Norman Patent Toolpost… not my design of course (probably Norman’s), but it seemed to tick all the boxes for rigidity, ease of mounting to the cross-slide, and the added bonus of being cheap.

There are loads of examples online, my favourites being this beautifully made example (how does he keep his workshop so clean?), and also this one from Morgan Demers’ blog (his site also includes an excellent and fascinating buildlog for a Gingery lathe, including loads of videos).

In my implementation of the design on the MD65/SD300, I wanted to preserve what little swing this little lathe has over the cross-slide. Also I wanted to use the existing four mounting holes in the cross-slide.

Construction method – workholding faceplate

There are many possible approaches to this, however I chose this slightly long-winded way because I felt it would produce the most accurate and tidy result. Also I struggle to produce a tidy and accurate hole with the mill boring head…

This make not make sense just now, but hopefully it will after you have finished reading the rest of this guide.

Boring of the hole in the baseplate, and also finishing of the brazed-together postblock and post, is done in the lathe. This has several time-saving and accuracy advantages over other methods, such as using the mill and a rotary table.

I had some spare 125mm aluminium round (leftover from the fixed steady), and used this as a workholding fixture for the toolpost. First I drilled and tapped three M6 holes so that I could attach the workholding faceplate to the lathe faceplate. I then faced the aluminium in the lathe, and also turned the outside diameter.

I used my CAD drawings of the baseplate to find the measurements for the counterbored holes in the rear of the workholding faceplate that will secure the baseplate . The dimensions are in the plans, however here is what it should look like.

A view of the rear of the workholding faceplate (the side that mates to the lathe faceplate), showing the M5 counterbored holes for holding the baseplate, and the three M6 tapped holes for bolting to the lathe faceplate.

As I say this will make more sense as you read the guide, but here is a brief description of each of the coloured holes:

  • Blue = Position A
    • Used to finish the post and baseplate after brazing
    • These fixing points hold the baseplate right way up (i.e. with the post facing out)
  • Green = Position B
    • Used to bore the hole in the baseplate (for the post), including the step
    • These fixing points hold the baseplate upside down (i.e. with the bottom of the baseplate facing out)
  • Orange = Position C
    • Used to turn the shapely curves at each end of the baseplate – these are required to ensure the baseplate clears the ways when boring the hole

I am a big fan of the workholding faceplate concept, and have used it for many other projects. Here is a pic of the current state of my workholding faceplate – lots of holes but still plenty of life left in it.

Top and bottom view. The one on the left includes three counterbored holes to attach to my rotary table. This side has seen some action as you can see from the mill marks – no problem I’ll just give this face a skim in the lathe.

Baseplate boring

The base plate is made using a slab of 60 x 105 x 12.7mm bright mild steel. Cut to size, and make sure you have a decent edge on two sides to act as a datum. Mark the two datum sides for reference (punch mark or engineers’ blue).

Now drill and tap the four mounting holes to M5. Also centre drill the location of the post (you will use this to set the block up in the lathe for boring the hole for the post).

Take care when centre drilling the location of the post! The diagram below shows the dimensions – the position of the post appears to be on the wrong side of the baseplate… however this is correct, as we will be boring the hole (and the step) from the bottom of the baseplate.

Now mount the baseplate onto the workholding faceplate using Position C (orange holes). I used four 1mm shim washers to hold the baseplate off the faceplate – this is not necessary but it does save the workholding faceplate from wear (I used these on all of the baseplate turning operations).

Mount the assembly onto the lathe faceplate. Use an HSS tool to turn the outside radii of the baseplate (carbide tools do not like interrupt cuts). Use 500rpm speed and take it slow… you may wish to shortcut this process by trimming the corners off with an angle grinder (or similar).

When you are done your baseplate should look like this.

Remove the assembly from the lathe, and remove the baseplate from the workholding faceplate. Re-attach the two pieces using Position B (green holes). Make sure that the centre-drilled hole is facing outwards.

Mount the assembly onto the lathe faceplate, and centre the work using a wobbler bar and the centre-drilled hole. Drill and bore the hole and step for the post (see plans).

Boring the hole and step for the post. The edge of the baseplate only just clears the ways – take care when setting up and swing the assembly the check clearance before switching on the lathe. You may also wish to attach counterweights to the spare holes to the right of the picture.

Turning the post

Turning of the post is straightforward. Aim for a loose sliding fit with the bore and step in the baseplate. The target gap will depend on the brazing rod you are using – check the manufacturer’s recommendations.

As described in the plans, turn the post 1mm oversize on the diameter, and 0.5mm oversize on length. Reduce to final size after brazing the post to the baseplate.

Also ensure that you centre-drill the top end of the post – this is essential for the finishing operation.

Brazing

Due to the sheer mass of metal, this is best done with the help of a fire brick or ceramic wool ‘cave’ – otherwise it’s likely your flux will go off before the work is up to brazing temperature.

I brazed my assembly with the post up (as in the photo below). Liberally position shaped lengths of brazing rod around the perimeter of the post and apply heat.

What a mess! Hey ho, I’ll just turn my troubles away… As you can see the braze went right through the gap and out the other side, indicating that it had penetrated all the way through. Note the centre-drilled hole on the top of the post. In the pic above I had leaped ahead of schedule and turned the boss on the top of the baseplate – you don’t need to do this.

Finishing the post and baseplate

If you have access to a mill you may choose (as I did) to fly cut the bottom surface. Otherwise, tidy the bottom of the assembly by rubbing with sandpaper set on a surface plate (or sheet of glass). Drill a >4mm hole in the centre of the base, to clear the 4mm post in the cross-slide (I did not try for a good fit on the post, I drilled my hole to 4.5mm to clear it).

Mount the assembly into the workholding faceplate using Position A (blue holes). Use a wobbler bar and the centre-drilled hole in the top of the toolpost to centre the work. Turn the post to final size and also turn out the boss around the post. The final thickness of the main part of the baseplate should be 8mm (see plans).

(Unfortunately I don’t have a picture of this final finishing – I hope the above makes sense).

Finally drill out the four mounting holes to 5.5mm, and countersink.

I would also suggest aiming for as smooth a finish on the post as you can manage. This will make for a closer fit with the tool holder and also make it easier to adjust the height. The exact diameter of the post is not important as we will be making holders to fit.

Making the toolholders and other hardware

Machining of the toolholders is straightforward and does not require much explanation.

I mounted the blanks in my 4-jaw chuck and bored a hole close to the measured final dimension of the post. I then test fitted the bore of the tool holder on the post after each pass. When I got to a tight sliding fit I stopped boring, and finished the inside of the bore with sandpaper.

I used a 12mm end mill to mill the large slot in the toolholders. You may choose to make a lever or other fancy arrangement to clamp to the toolholder to the post – I chose a simple M8 capscrew as the allen key for this is the same as those on the tailstock, and is therefore always close to hand.

The only real decision to make with the tool holders is which side to mount the clamping screw. I made one of each, and find that each one is better suited to some operations. For example, if the clamp bolt is mounted on the left (as per the pic below), the capscrew head can get in the way when boring.