Sunday, 29 March 2020

Mini-Lathe - QD Splashback

Accessing the slide for adjustment was always a problem. because you have to remove the splashback. This is easy enough but as standard it is retained by five short M5 screws, which are a pain to replace and resulted in me not checking the carriage adjustment as often as I might:

Here's the back of the lathe without the splashback in place:

I changed these for studs and long sleeve nuts, which means I can remove and replace the splashback, by hand, without moving the lathe at all. The studs are M5, about 50 mm long and are retained with Loctite 243 thread lock.

The sleeve nuts are made in two pieces:

  • a short (13mm) brass thumb nut, threaded M5
  • an 8mm OD aluminium sleeve, bored 5.5 mm which is fixed to the thumb nut via an interference fit in a counterbore in the thumb nut. The sleeves are opened up at one end with a centre drill to maximise the capture funnel

Here they are in place:

The fifth fixing screws into the head stock under the chuck and has to be long enough to reach with the chuck in place. Because its axis is parallel to the lathe spindle, you can't use a stud so this is made from a piece of studding in a long extended nut.

You can see it in position here, a bit more visible with the collet chuck in place:

Thursday, 26 March 2020

Mini-Lathe - Cross slide lock

Mini-Lathe owners are forever chasing ways to stretch these little machines and many modifications are aimed at making them more rigid. It's always a challenge to remove play from the cross slide, but still have it easy enough to operate without strain leading to pain in your hands.

A good option is to add a couple of screws to load the cross slide gib - you don't want to mess up the adjustment, but adding two screws means that a temporary lock can be provided and the machine returned to normal settings very easily.

The cross slide is cast iron, which is easy to drill and tap:

Watch for the drill catching as it breaks through on the 30 degree feature inside.

These are tapped M4, and I've marked the ones used for locking with an 'L'.

Here it is in situ. I've changed the grub screws that are used to lock the slide to cap heads - to make it obvious which ones you use.

Wednesday, 11 March 2020

QR50 - Fork Bushes

As you know, I have decided to make a new set of telescopic forks for the QR50 since I can't find a new pair locally, or anywhere else for that matter, for a reasonable price. You've seen how I recovered the sliders and stanchions with new tube, and replaced the missing dust caps with machined parts.

Now it's time to machine the bushes and assemble the bits. I bought a 30 cm length of 30 mm white acetal, and cut off two 80 mm lengths, planning to make a complete leg-set of bushes in one setting. I wanted to make sure the set-up for the 22 mm bore was done without removing the material from the chuck.

I made a drawing to set my bush lengths against the existing design and the springs I had bought:

I set one of the 80 mm lengths up in the 3-jaw and centre drilled it, opening it up through 6, 10, 13  and 19 mm for the boring bar.

Here's the boring bar in action, taking out a 40-45 mm length to 22 mm or so to give a sliding fit on the stanchion.

From this bored part, I finished the top bush OD to 29 mm and parted off.

The top bushes fit in a 29 mm ID register in the slider, which is made from 32 mm OD seamless tube of 2 mm WT. The bush has a 0.5 x 0.5 mm register in one end to let it sit just below a circlip groove in the slider.

The circlips are wire type - I bought the sheet metal type initially before I realised there wasn't sufficient space in the leg to house them. Wire types are harder to get out but occupy much less space. The nominal 30 mm circlips need the ends trimming:

The clips fit in the end of the slider nicely - there is a 0.5 mm deep groove about 8 mm in, to let the clip retain the top bush:

The slider has a ground channel to allow you to get a scriber under the circlip:

It's very hard to see, but the circlip ends are ground flat to allow you to lift the ends out of the grooves:

The bottom bush is essentially a blind tube - bored 22 mm for the stanchion and finished to 28 mm OD for the slider, it has a 5 mm thick closed end to seat the spring. It's loosely retained to the stanchion with a small roll pin.

This shows the complete assembly, with the dust cap, main compression spring and the rebound spring. The springs were bought from ebay, selected for wire diameter and OD.

Here's the stanchion in paint:

The frame is also almost finished:

By the way. This interesting effect is called fisheye, and is what happens if you don't degrease the parts prior to painting...