Member postings for Andrew Johnston

Spent part of the day roughing out the LP cylinder liners. The extruded cast iron was turned 0.1" over on OD and 0.1" over on length. It seemed a shame to machine away the central slug so I chain drilled from both sides to remove it. A simple spreadsheet allowed me to select a drill size that would give about a 2 thou or so overlap between holes. The drilling in progress:

After drilling from both sides a couple of sharp taps with a hammer and the core broke away. The two LP liners roughed out, OD is just over 4":

In total 104 8.4mm holes and 3" deep. Thank gawd for the bolt hole function on the DRO and power down feed on the quill. I chose a conservative 3 thou per rev at 800rpm. Each hole took just over a minute. I did try the 6 thou per rev feed but it seemed a bit much driving an ~8mm drill with no pilot hole. In addition, by repute, the quill power feed on the Bridgeport is a weak area, so no point in pushing it. Next job, tomorrow, is 60 holes for the HP liners.

I also coughed up the money for having rubber tyres vulcanised on one set of wheels for my traction engine. I hope to collect them in the next couple of weeks.

Andrew

Well so it is, never knew that. I'd just assumed it was cast iron. The lathe will be lighter than I imagined; although I've never found a definitive spec for the weight.

Not sure what you mean by a clutch? My Britan has a lever clutch to engage high or low speed ranges, but that's not the same as a clutch to stop/start the spindle. These were production machines designed to run continuously. With operators on piece work I doubt they would have used a clutch to stop and start the spindle on a regular basis.

I don't know what the collets are made from. I'd guess a medium carbon steel and hardened to something like 40-45Rc.

I had some 3/4" collets, but sold them yonks ago. Good luck and have fun with your lathes. I assume that all accessories, apart from the collets, are interchangeable between the 3/4" and 1-1/4" machines?

Andrew

This link may clarify the connections needed:

**LINK**

Note that the switches control contactors, they do not switch the phases directly.

Andrew

So what unalloyed high carbon steel are you comparing it to?

Andrew

Another illusion shattered; I though silver steel was a high carbon steel.

Andrew

Based on what evidence?

What has actually happened is that semiconductor junction has been overheated and the doping levels have gone pear-shaped. So the junction no longer operates as a diode. You'd see exactly the same effect (albeit with different voltage/current values) if you repeated the experiment with an ordinary silicon diode.

Andrew

As mentioned 1050 is almost pure aluminium. As far as I'm aware it's only available as sheet. I've used it a fair bit for sheet metalwork as it bends nicely without cracking, unlike some of the alloys. But due to it's horrid machining characteristics it's one of the few times I use old school marking out with hand drilling and filing to work it.

SoD seems to have looked at a rather odd selection of alloys. The other common alloy, 2014A (aka HE15), is listed as excellent for machining.

Andrew

Of course it depends upon the exact type of steel, but as a starter, with insert tooling, I'd be running at 1200rpm and 0.1mm/rev for finishing and 0.2mm/rev roughing.

Andrew

Postscript: My lathe doesn't run fast enough to use recommended surface speeds on 20mm diameter aluminium. I might up the speed to 1700rpm but keep the same feeds. I would change the insert to a CCGT aluminium specific one.

Edited By Andrew Johnston on 23/08/2020 21:35:42

I don't know what mpm is, but 80m/min is never going to be a sensible feedrate on a lathe, or even a mill for that matter.

My advice would be to ignore information online, a lot of it is worthless and/or just plain wrong. Tell us what you want to do (material/diameter as a minimum) and I expect we can come up with some sensible spindle speeds and feeds. I would think that the gearbox on your lathe will list distance per rev in some positions, as well as tpi.

Andrew

I did all the boring and grooving on my eccentric straps and sheaves on the lathe using fixtures in the 4-jaw chuck. The assembled eccentric straps were located with four buttons for boring and grooving:

Similarly the sheave was mounted on a plate for boring the offset hole:

The plate is set true by indicating on the central hole. Not visible are two buttons at positions calculated to give the correct offset for the hole in the sheave.

Andrew

That would have been useful when I had to machine a 72 tooth gear:

Andrew

6082T6 will be a much better choice. It machines very well although a squirt of WD40 may be needed to avoid the swarf sticking to the tool.

Andrew

Rather you than me; 1050 is absolutely horrid to machine as it's essentially pure aluminium. It behaves like soft fudge, but doesn't taste as good. It moves rather than cuts and leaves large burrs.

I'd buy the cheapest HSS cutters you can find, as you'll be breaking some of them. There's no advantage in using carbide and unless they're highly polished carbide might be more prone to BUE.

Andrew

Good grief, that sounds too hard for me; I'd better not try building anything.

Andrew

I'd agree with Clive. You don't need the properties of SG iron and in my experience it has a great propensity to chatter, whereas ordinary continuously cast iron machines very nicely, if rather muckily.

Andrew

Brian: I don't understand your last post? In my experience running a 2-speed motor on a 3-phase supply (which Tom has) works just fine. I'm not sure where starting on 2 phases comes into the picture?

Andrew

I finally got around to machining the cover plate for my traction engine regulator. It took some experimentation, and broken cutters, to get a result. I started with two 0.5mm 2-flute cutters from Drill Service, albeit their economy range. In all cases the cutter was running at 24000rpm. I started with a stepdown of 0.1mm and stepover of 75% and a feedrate of 80mm/min. The cutter started well but broke about half way through a 2 hour program. With the second cutter I dropped the stepdown to 0.063mm and the feedrate to 40mm/min. The cutter finished the initial machining but broke at an undetermined point. The finish left was poor with ridges and uneven surfaces.

I then bought two 0.5mm 3-flute K2 carbide cutters from Cutwel. After machining the basic outline the original program cuts the centres of the O and P. These are very small openings, not much bigger than the cutter. I was concerned about stiction on the table possibly overloading the cutter. So I changed the program to remove them, changed the stepdown to 0.05mm, the stepover to 60% and increased the feedrate to 120mm/min. The program took just under 2 hours and ran to completion without breaking the cutter:

I then ran a separate program to open out the O. I didn't push my luck with the P. On the cast cover on the fullsize engine the P is solid - so I can argue I'm sticking to prototype.

I'm pretty impressed with my CNC mill; it's by no means new and has been worked fairly hard yet it seemed to be happy with a small cutter where every tenth counts.

Tomorrow I'll see if I can salvage the original cover plate, or whether I'm going to have to make and profile another blank.

Andrew

Dooooh!

Andrew

A 1" thread is nominally 1" OD. In practise you might need to skim a thou or two off to get a good fit. But if the thread in the backplate is 22mm maximum then it ain't a 1" thread of any variety. If by "maximise" you mean the ID of the backplate thread then that's not far off correct for a 1" x 8 thread, albeit slightly large. How do you know you cut the external thread to the correct depth?

Andrew

Bought on Ebay if I recall correctly? Quite possibly factory QC rejects that then get sold on the grey market to unsuspecting consumers.

Andrew