Member postings for Andrew Johnston

I apologise if anyone took umbrage at my earlier throw away remarks about apprenticeships.

I've played with one of the old C-type chucks, as I ground a new centre for the owner, but never used one in anger. All my Clarkson chucks are the later S-type. I've never had a problem with the nut sticking, even on the larger ones I use on the horizontal mill.

Andrew

Exactly, and that's how better techniques can get ignored, or looked down on. Although at one point I was looking at apprenticeships, due to an impending academic car crash, in the end I'm glad I didn't do one Instead it means I have to work it out for myself, mistakes and all. And I'm happy to try new ideas like CNC.

Andrew

Assuming one doesn't have an independent means of measuring the bore how does one know when one has the right technique?

Andrew

Got a set somewhere, but can't immediately find them. Which about sums it up. I much prefer to use proper internal micrometers.

Andrew

I'm currently using my hydraulic copy attachment to screwcut tapered threads. I'd like to control diameters a bit more consistently than I've done in the past. On the attachment is a silver knob with indents marked from about a thou to 60 thou. In this picture it's the silver knob above the lettering 'Colchester':

The manual says it's a micrometer for adjusting the final depth cut. Simplistically I would expect moving it would move the slide slightly thus adjusting the cut depth even with the follower fixed. But it doesn't. So I don't know if it's broken or I don't understand how it works.

Can anyone offer any insight into it's operation?

Andrew

IIRC there was a discussion here some while back as to whether the thread form on a tapered thread was perpendicular to the axis or to the taper. I'm happy that's it's to the axis; especially for BSP which can mate with a parallel thread.

I can't see much difference between a 19W insert (lower) and a 3/8" BSPT insert (upper):

Other than, possibly, the trailing crest curve. The difference in height between successive crests for a 3/8" BSPT thread is about 1.6 thou aka not a lot.

I started with a parallel cylinder, worked fine. I've made a CAD model of the plug so I know what the maximum thread diameter needs to be allowing for some stick out past the gauge line. I just turned the cylinder to the maximum diameter, give or take half a thou.

Andrew

Seems rather a mix of materials? What scale and type engine, and what boiler material? On my 4" Burrell SCC (steel boiler) I have made EN1A nuts. I won't be using washers as they're not prototypical. I've partially made the studs from EN3B which is normally recommended, although not without dissenters.

Andrew

The diameters listed don't seem to tie up with either minimum head diameters or the maximum theoretical sharp head diameter, which would be needed if the head is to be flush?

Andrew

A proper taper turning accessory was made for my lathe, that allowed the cross slide to be adjusted with the dial whilst also turning a taper. However, complete sets don't come up for sale very often and are silly expensive. So I used the hydraulic copy unit with a hand filed template:

The insert is indeed full form and is specifically for BSPT, not just plain old BSPP. The angle on the template isn't too critical as the mating bushes in the boiler are BSPP, rather than a matching BSPT thread.

A CNC lathe would be a nice to have. But the hobby level machines without live tooling and servo controlled spindles don't really offer me anything that I can't do with the hydraulic copy unit and repetition lathe.

Andrew

It rings a vague bell, but I can't remember where I've seen one before. A diamond shape doesn't preclude holding round objects like drills, and may have been a way round the patents for Jacobs style chucks.

Andrew

The lug is part of a serrated pin that holds the shaft on the lever to a collar with slots in it to drive the contactor. If that's not clear I can take pictures, or create a sketch.

Andrew

Been there, done that and broken the centre end on a 1/4" cutter.

I'd also agree that there should be no gap between the nut and body. Instructions here:

Andrew

Screwcut my first tapered thread, 3/8" BSPT, so 19tpi and Whitworth form with rounded crests and roots, for blowdown plugs. This is the trial, in brass, rather than expensive bronze:

Ok, but not perfect, I need to do a bit more fine tuning of the technique.

Andrew

Trial and (hopefully not too much) error for me. I normally countersink manually with the work on the mill table. I have a fairly good idea of the depth needed so I set a bit less on the knee, countersink and try a screw. I then raise the knee in 0.1mm or so increments until the screwhead is flush or slightly recessed. Then, with the knee and quill stop set, the rest of the countersinks should be consistent. For paid for jobs it isn't that important as long as the heads are slightly recessed. I don't use many countersink screws on my model engines, and those that are there are hidden. The last countersinking I did was for M12 on this steel plate, used to fix the broken bench that the flypress sits on:

Andrew

Logic is good as far as it goes. But you can't open the door with the lever in the ON position. The only way to open the door is with the lever in the OFF position, which is where you wanted it in the first place.

Andfrew

Pictures need to be uploaded to an album before inserting in a post. Here's a link to a "how to post pictures" thread:

**LINK**

Andrew

Pictures of the lever and spring, in the OFF position:

And the ON position:

The spring is pretty weak, wouldn't pull the skin of a rice pudding. The geometry is such that the spring tends to move the lever to whichever setting is selected. It certainly won't return a lever in the ON position to the OFF position. Given that you can't open the door with the lever ON I can't see why you'd want the spring to return the lever to OFF?

Andrew

Errr, it's a jig borer, not a milling machine. Of course one can use it for milling, but that's not it's purpose. It was intended for the accurate placing of holes for jigs and fixtures. It would be capable of working to a tenth or so, long before the days of DROs

Milling machines go far bigger than the picture in the link. Search for bed mills.

Andrew

I'm not familiar with the mill, but 3, 4, 5 and 6mm are standard shank sizes for milling cutters. Likewise 2.35mm is about 3/32" and 3.2mm is about 1/8". So I would have thought cutters from any source with those shank sizes would do.

Andrew

Yes, but not right now as I'm going to do a bit more gardening before it honks it down over the next couple of days. I'll give mine (also on a MG12) a clean and take some pictures tomorrow morning.

Just a thought, is the spring you mention on the handle on the door, or on the isolator proper inside the cabinet?

Andrew