Member postings for Andrew Johnston

Possibly to distinguish them from side and face or slab cutters as used on horizontal milling machines.

Andrew

Not really, it just reflects a closed mind and assumes that there is a right and wrong answer, which is rarely the case. Engineering doesn't work like that; it's as much an art as a science.

This thread is a case in point. It started with a general enquiry about learning manual machining. It then transpires that the OP is interested in building a large scale traction engine. That helps narrow down the advice given, and may make earlier posts seem less relevant.

Andrew

Exactly, I use thread depth as a guide, but use a mating part as a gauge for final fit. I aim to achieve a shake free fit, and agree that a couple of spring passes can be the difference between go and no go. For brass and cast iron a brush to remove swarf dust also helps. I rarely use dies, many external threads are screwcut, or done using Coventry dieheads.

I screwcut a lot of 32 and 40 tpi ME threads, where thread depths are small, A few thou can be the difference between a shake free fit and a rattling poor fit. My ME taps and dies are old and carbon steel, so it's not clear that they are particularly accurate. Consequently trial fits are essential.

My original comment in response to Clive's comment was partly tongue in cheek. My lathe is ex-industrial and I have an Ainjest unit fitted. The unit was bought on a whim, just to experiment, but I've found It makes screwcutting, especially blind internal, much easier, and faster. So I don't see it as cheating. I use techniques that are appropriate to the machines that I have. I distrust people who are dogmatic about the right, or wrong, way to machine something. I recall a forum member telling me that CNC milling wasn't really true modelling, until they got a CNC mill that was.

Andrew

I was picking up on the spelling rather than punctuation, but also thought the thread could do with a little levity.

Andrew

Nothing wrong with medlars, got one in the garden. They look horrible after bletting, but taste lovely.

Andrew

More fool them, but they probably also regard the electric motor as an invention of the devil.

Andrew

A few pictures for interest, milling the edge of tooling plate, 25mm thick, with a (worn) 10mm carbide endmill. First, conventional milling and cutting dry:

Climb milling, cutting dry:

And conventional milling with a squirt of WD40:

Andrew

I wouldn't start from here. The cutters look to be poorly ground on the end, although both are theoretically capable of plunge milling. I buy cutters from professional tool suppliers. At least one can then be assured that they are properly ground. On a slot drill one edge is ground for the full radius for plunge cutting, the other edge is shorter:

Similarly 3 and 4 flute cutters intended for plunge cutting have one edge at full radius and the others are short. The only professional cutters that I have seen with two, or more, cutting edges at full radius are those with radiused corners, intended to provide an excellent surface finish on final facing cuts, like this:

Low power mills need all the help they can get, which is why I use professional cutters.

Andrew

Anything is better than nothing. When I was a kid, and a member of the Bedford Model Engineering Society, one of the members had a small workshop in the back of his greengrocers shop. It was tiny, can't have been much more than 4 or 5 feet square. But it didn't stop him building models.

Andrew

When I was looking for an angle plate I only considered the second pattern. All round much more rigid, and easier to adjust. Can't help with precise size requrements, as mine was bought secondhand. It's knocked about a lot, and is a tad on the large side for the Bridgeport (10" x 18" ), but nothing is going to shift it while machining:

Andrew

When I considered how to power my Harrison M300 and Bridgeport mill I weighed up the options, and in the end decided to go for a proper 3-phase supply, Although not particularly cheap I needed to upgrade the incoming supply anyway, 60A plus a wind yer own fuses box. In retrospect it was a good choice as it makes it simple to run the two speed motors that some of my later machine tools have plus all the ancillary motors. If I ever get an electric vehicle it will make charging quicker.

An inverter inherently generates conducted emissions on the mains and radiated emissions on the motor cables. However, both are simple to deal with, using off the shelf filters for the mains and shielded cable for the motor connections. I have 2 inverters on my CNC mill and have not had any problems with noise or unwanted tripping.

Andrew

This is a 3/4" BSF thread screwcut with a carbide insert plunging straight in:

Can't remember at what spindle speed, but not fast, probably 125rpm. Finish looks ok to me. Finish cuts would have been a couple of thou DOC.

Andrew

I agree with Clive, the rollers are mostly likely cast. Helical milling (not spiral) doesn't help in forming what look like sharp internal corners on the "teeth". I expect they could be done, to an extent, on a 4-axis CNC, but it wouldn't be economic, for me at least.

Andrew

I don't mess about setting the topslide at an angle when screwcutting, but leave it set parallel. The cross slide can then be simply advanced by the required thread depth. Only one number needed, and one handle to twiddle.

Andrew

It was meant to be serious. My bad for mentioning engineering on a modelling forum.

I made the assumption that if "old mart" had a 59 hole plate available he would have had the wit to use it. Assuming a 40:1 dividing head the indexing needed at each step is 40/118, times 9 to the get the answer in degrees. One can use the prime factorisation theorem to simplify to 20/59.

The easiest way to make the plate is using a DRO with a bolt function, which is what i did. But there are other methods which do not need a DRO - see one of the Bedside Readers, can't remember which volume. Any errors in the radial placement of the holes will be reduced by a factor ot 40.

Andrew

Simple enough to make one, index 20 on a 59 hole plate. Here's one I made for 63 and 69 divisions, as I was too idle to set up for differential dividing:

The ideal set up would be a dividing head and a horizontal/vertical rotary table. As discussed by JasonB they have different strengths and weaknesses.

Andrew

No problem, I wear steel toecap shoes in the workshop.

Andrew

No, it's for butane; you need propane. Temperature and heat are different things. Many of the small torches will reach the required temperature for silver soldering, but will not be able to supply enough heat. When I started silver soldering I had all sorts of problems, even with a Sievert torch. Turned out I didn't have a big enough burner, ie, not enough heat. By the time even small work got up to temperature the flux was exhausted. I second Sievert and propane.

Andrew

+1

I only use the quill for drilling and boring. For all milling the quill is retracted, and locked, and Z feed put on by raising the knee.

Andrew

There seems to be confusion over measurements; 0.02mm is not 8 thou, more like 0.8 thou. On my (industrial) lathe putting a cheater bar up the spindle and pushing/pulling as hard as I can resulted in no movement when pushing down, and 0.01mm when pulling up. So 0.02mm of movement isn't great but probably won't be noticed. If the movement is 0.2mm then something is seriously wrong.

The forces generated when turning can be surprisingly high. The formal way of showing them is with the Merchant diagram. When turning the workpiece is trying to pivot up and over the tool point. Let's look at the torque available. My lathe has a 2200W motor. Suppose we're turning 25mm diameter bar at 500rpm. Spindle speed of 500rpm is equivalent to 52.4 radians per second. So the maximum torque is about 42Nm. At a radius of 12.5mm that produces a maximum force of 3360N, or ~336kg.

Andrew