LBSC Titch help and translations please!

Ok, I am in the process of dusting off my titch that's been sitting in a box for over 20 years.

I have been working my way through the book....

What does "pin drilled" mean? Is it the same as counterbored? and do I use a counterbore drill for that or do it some other way?

The book is not really clear on this.

Also, my mill (SX2P) is a very good precision drill, and its also a pretty good fly cutter but I seem to have a lot of bother cutting slots. if you were doing this, would you just buy laser cut ones?

Peter

If you are referring to the slot in the expansion link then laser cutting is not the way to go. Laser cutting is precision gas cutting, it leaves a very hard but rough (at a microscopic level) surface and would wear the die blocks very quickly.

Are you using slot drills? using an end mill to cut a slot can be problematic.They almost always cut oversize, and you can't plunge them in if the slot is blind ended.

Hi Peter,

'Pin Drills' are indeed like counterbores but usually with 4 teeth/cutting edges, and made out of silver steel with a pegged insert for the hole. In years gone by all the ME suppliers sold them, especially Kennions. I have quite a few that I use very regularly on certain jobs.

They have the advantage for those without a mill that they can be used in the pillar drill once the appropriatte hole has been drilled.

They can also be used in a handrill.

What bit of Tich do you need to cut slots? Apart from the ports on the top of the cylinders I cant think of much else on Tich that requires slots involving the problems you describe.

Cheers,

Julian

Yes, its the curved slot in the expansion link although I also need to cut a couple of slots in some gauge plate for a clock I am making. Something just isn't right. the cutter seems to want to jump. maybe I am trying to take off too much at a time but I don't think so. It just doesn't seem to work for me.

I am ok with the steam ports. I actually had an old Trojan cylinder knocking about and I used that to practice on the other day. I was actually pleasantly surprised at how well they turned out!

Julian, I have checked the usual suppliers, can you suggest somewhere I may be able to get a pin drill?

Peter

Hi Peter,

You dont really need pin drills these days if you have a vertical mill and a goodly supply of decent slot end mills. I havent seen pin drills advertised for quite a few years. They are very useful on non ferrous stuff in making boiler fittings though.

For the expansion link slots I have always chain drilled them then filled the slots in gauge plate. I can usually do a pair in one evening. I have never milled them, though I have the capacity to do this.

Cheers,

Julian

A pin drill can still be quite useful, for instance where the hole to be counterbored would require a really long cutter to reach it. This can be the case for instance on some of the Stuart engine standards. They are dead easy to make, which also means they will be the size you want. The technique is to take a piece of silver steel the diameter and length you want. (or turn down a slightly bigger one). Drill the end with a hole the size of the pin you want, eg to be an easy fit in the hole to be counterbored. Now take a fine triangular file and file the cutting teeth in the end. This can be done by eye. Make sure you file them so they will cut with the correct rotation direction. The idea is to file the teeth such that the sloping back just meets the front cutting edge without leaving a flat and without taking anything off the height of the tooth. Work your way around until you have cut teeth all the way around. They probably will not be even but that is not a problem, it helps prevent chatter.

Next heat the business end with a torch by playing the heat back from the teeth a bit until the whole end is the colour of a boiled carrot. They used to say cherry red, but most cherries are not the right colour! Keep it at that temperature for a minute or so, then plunge the hot end into cold water. Now it should be very hard, and will also be brittle. You can check the hardness with a file, it should just skid on the surface. Don't drop it, it will be very brittle at this point. Use some wet and dry paper to polish off the blackening of the surface, then heat again a bit down from the teeth. You should be able to see colours start to run along the surface away from the flame in both directions. When the pale yellow (Light straw) colour reaches the cutting teeth plunge it in the water again. It should now be capable of cutting, so fit a pin into the hole and try it out. I have made quite a few of these and have used them on steel, cast iron, and aluminium with great success. They should not be run too fast as they are not high speed steel of course.

If you are not happy with the tempering, you can heat the whole thing up again and reharden it. I have never had to resharpen one, they only get very occasional use, but if you need to you can soften the whole thing by heating it up and then cooling very slowly. They used to leave them overnight in the ashes of a coal fire but most people don't have one of them anymore.

John

I've made them by turning the pin on the end and making enough undercut that I can file the teeth right across. Obviously this is limited to pins down to about 3/32" so not good for very tiny ones.

They can be remarkably crude - see below - and still work. the bottom one has a conical end for boring out nipple unions.

Neil

Many thanks for your help guys.

Question from a thickie.... Out of curiosity, can the smaller laser cut parts be normalised to get rid of that hard skin?

Peter

according to **LINK**

the surface hardness is at least partly due to a thin layer of oxide, so normalising wouldn't remove it. If you look closely with a loupe, you'll find that even if you could soften the hard layer, the surface finish is poor, so you'd have to use a file to get a decent finish. Like Julian I have filed expansion links by hand, not too difficult. On my second loco I machined them on a big rotary table, on the third had them wire eroded (someone owed me a favour). For a Tich, I'd bin the valve gear and use slip eccentric.

Edited By duncan webster on 21/10/2016 10:59:55

Why rely on laser? Water jet is totally non hardening.

Regards Ian.

Where's the fun in that