Colchester Student Rear Toolpost help needed

[Preso]

I have a Colchester Student Mk1.5 in good condition but I am really keen to fit a rear toolpost so that I can leave a parting tool set up more or less permanently. I have been looking for a long time to purchase one on Ebay but it seems they are quite rare. I suspect that anyone who owns one is not likely to give it up. I have an illustration of one in the Colchester Student Spare Parts and Accessories book and I have modelled most of the parts in my CAD software. I am hoping that I can get castings made but before I make the patterns I was hoping to get some accurate measurements of the tee slots, tool slots and a few other features that might be critical to the design. If anyone out there has one and is willing to share the dimensions of it I would appreciate it.
Regards,
Mark Presling

[plunger]

Hi Mark >if you dont come right I may know two guys who own the same lathe as you for dimensions. But what i dont understand is why you need to cast anything at all .unless you mean you want to cast the entire crosslide . I think these colchesters came out with two different saddles . I think the carriage wheels are even on different sides .Otherwise if you dont need a new crosslide why cant you just machine it from a chunk of steel. ?

[Ian B]

+1 on the "machine it from chunks of steel"; quicker, cheaper and stronger. How does it attach to the cross slide - does yours have existing tee slots? I have a Harrison M400 that has vee profiles along the outside edges of the cross slide, these would be ok to hold something like this in place.

For dimensions, just make them up - the bottom of the tool mounting slot will need to be a bit below centreline, giving you the option of shimming the tool to the correct height. For this, I'd use M12 bolts throughout. I once made one for a Myford ML10, just over engineer it, you'll be fine.

The only things putting me off doing something similar are:
1. I keep my insert parting tool in a quick change holder, it takes seconds to mount it.
2. Having a parting tool there looks like it'll hit the chuck during normal turning sooner or later.

Ian

[jimsehr]

I think Hemingway has a kit for those.

[plunger]

I did this for my emco v13. A rear mounted parting tool holder. but it has no adjustment. I designed it for an iscar parting tool holder and did it upside down. the reason for this is it works better upside down (Ive been told)and also I dont have to change rotation of the spindle.

[tom_d]

Don't need to get too fancy here. All that's needed is a block of some solid material mounted to the cross slide. mill a T-slot that will be parallel to the lathe bed ways. Size the T-slot to be similar to what's on the lathe's compound. Shop around for a used turret tool post sized for your lathe to fit that block. When determining the thickness, or height of the block, make it so that a tool mounted in the turret post sits about 10mm below lathe center line. When you mount the turret tool post have it sit on an approx. 10mm spacer. The spacer can be made from aluminum. In final use the spacer can be swapped out to different ones of various thicknesses to place tools on center height. Experiment with placement of the block on the cross slide to determine best location before drilling the mounting holes in the cross slide. You may want a few hole patterns in the cross slide to accommodate the size of future projects you make. The block that holds the tool post can be made from aluminum, or some steel alloy if you want to make it more durable.

[754]

On my British turret LATHE ... AKA Capstan, i made one out of 2 x3 Steel .. standing up. Bolt thru middle for tee slot, milled on bottom to look like a key. You could use 2 pins the size of T slot groove pressed into the block.
You can probably mill the slot on the side, by running block past an endmill mounted in the chuck (if you have no mill ) SHIMMING REQUIRED..

[Preso]

Thanks for the replies. Just to clarify a few things, I know a guy who does casting in iron and he has agreed to cast the two parts that I need. He has a Colchester Dominion lathe which is very similar to the Colchester Student and we are planning to do a YouTube collaboration where I make the patterns and machine the parts and he does the castings. The plan is to make a pair of these tool holders, one for each lathe. Before my collaborative partner came on board I did consider making the tool post from steel sections but finding small pieces of good quality steel where I live is just about impossible. The reason I would like to have a rear toolpost is because you can mount a screw cutting tool in the conventional manner and cut left hand threads away from the headstock. Also a parting tool used in a rear toolpost is a lot less likely to dig in or misbehave. If the toolpost might foul on a part in the chuck when using the conventional QCTP it is a matter of loosening two nuts and the whole toolpost can be slid off it's base. I wanted to make it as close to the original Colchester pattern simply because it would look right on the lathe and I am guessing that the Colchester engineers thought the design through and it should be optimised for that lathe. I have had a response from another source and I am in the process of changing my model and I will do a mockup in wood before going to the trouble of making the patterns.

[Ian B]

Would this be what you're looking for? https://www.ebay.co.uk/itm/Lathe-rea...sAAOSwLe9gEow1

Here's another, just the tee slotted base: https://www.ebay.co.uk/itm/Lathe-rea...MAAOSwvoxgAF6e

Ian

[dian]

why do you need the lower t-slot block?

[Ian B]

I think it allows you to fit "different things" to the back of the cross slide - but apart from a parting tool rear holder, I've never seen anything else mounted on the tee slotted block. It does let you adjust the position of the toolholder in 2 axes, which is handy.

Ian

[754]

While you are doing it, mayas well cast a few extra ones..

[old mart]

You could use SG iron casting, but I would just machine it from a single piece of mild steel, or two pieces if the tee slotted base was important.

[andywander]

...The reason I would like to have a rear toolpost is because you can mount a screw cutting tool in the conventional manner and cut left hand threads away from the headstock.

If you mount a thread cutting tool in a rear toolpost in "the conventional manner" (which I guess means not upside down?), and cut away from the headstock, you will get a RH thread.

To get a LH thread while cutting away from the headstock, you need to mount the thread cutting tool in a front toolpost in "the conventional manner".

[old mart]

And if you get a lefthanded internal threading tool, you can cut righthand threads away from the chuck running in reverse. The main reason for a rear toolpost is for parting off with the tool inverted.
With a righthand internal threading tool, you can cut lefthand threads away from the chuck, running forwards.