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Member postings for Andrew Johnston

Here is a list of all the postings Andrew Johnston has made in our forums. Click on a thread name to jump to the thread.

Thread: Clarkson dedlock
13/06/2020 09:50:55

Never seen one, so possibly not; mine is INT40:


From a practical point of view I suspect most R8 fitted mills wouldn't be capable of utilising a Dedlock cutter. I certainly wouldn't use this cutter on my Bridgeport:



Thread: What Did You Do Today 2020
13/06/2020 09:45:49
Posted by Neil Wyatt on 13/06/2020 09:31:01:

You need to present your data as 0 to 359 or 1-360...........

That takes me back to the great zero-one controversy. Many years ago when I was designing active noise control systems I labelled microphone inputs and speaker outputs from 1 to N whereas the softies labelled them 0 to N-1. For the first system I designed N was 64. That's a lot of hardware when the boards were wirewrapped or point to point wired using the expensive Verospeed system.


Thread: Spilt line for direction of TE crankshaft bearings
12/06/2020 23:15:07

Bother, when I was posting I had a premonition that I was going to end up looking a wally. And so it came to pass. embarrassed


Thread: 3 Phase in a Model Engineers workshop
12/06/2020 23:12:56
Posted by Martin Connelly on 12/06/2020 22:59:50:

............the machine was running on a domestic 3 phase supply........

What's a domestic 3-phase supply? I've got 3-phase in my domestic garage and it's definitely 415V phase to phase.


Thread: Spilt line for direction of TE crankshaft bearings
12/06/2020 21:59:50

Crankshaft bearings are split horizontally. Otherwise it would be difficult to assemble the engine.


Thread: Parting off
12/06/2020 21:22:51

Here are the results of some turning trials. Material was 25mm diameter EN1A and a CCMT insert. Spindle rpm was 1200rpm,and depth of cut 0.1". I did two tests, one with a feedrate of 4 thou/rev and one at 8 thou/rev. I then measured the width and thickness of the swarf:

4 thou/rev width = 0.098" thickness = 0.007"

8 thou/rev width = 0.117" thickness = 0.010"

Somewhat inconclusive on width, but we can say that the chips do not get thinner. It would seem strange if they did as it's not clear what force would be pulling the chip away faster than it is being generated.

I also looked at the swarf generated by a 3mm wide insert parting tool:


The insert curves the swarf and in particular curls the edges to make a shallow channel. The width of the swarf was about 0.117". So only a gnats wotsit less than 3mm.

As an aside all the swarf was quite brittle, which is not a quality one would associate with EN1A. May be it's a consequence of the shearing action?

I'm aware of the claimed advantages of rear toolpost parting; my question to David was about why the forces are different in parting off as opposed to turning. If we assume a square parting tool I would expect the force vector to resolve to two orthogonal forces. There should be no force parallel to the axis of the work. Depending upon material and tool shape there might be a force perpendicular to the work axis pulling, or pushing, the tool into, or away from, the work. But the main force will be downwards. It seems all wrong to react that force upwards trying to pull the cross slide off the saddle and the saddle off the bed. The machine designer has gone to a lot of trouble to make the bed stiff in order to resist downward forces so why not make use of it?

A claimed advantage of rear toolpost parting is that the swarf falls away. That may well be true for brass and cast iron but for steel where the swarf may be slightly wider than the tool the swarf is so light that the force on it due to gravity will be negligible.

Front parting works fine for me so I'll stick with it. smile


Thread: What Did You Do Today 2020
12/06/2020 17:22:36

After the interregnum caused by the horizontal mill feed gearbox 'noise' both cylinders now have four faces machined square and to consistent dimensions, plus the sides of the flange have been cleaned up:


It's now over to the vertical mill (and DRO) to machine one more reference surface and then start machining cutouts, bores and tapped holes for studs.

It turned out that the loose motor cooling fan was the cause of the gearbox 'noise'. That's a relief in one sense, as it was an easy no cost fix. But if I'd known that from the start I wouldn't have needed to dismantle everything. I could have got to the fan simply by removing the sheet metal cover round the motor.

Not sure when I'll get back to the cylinders as it looks like the weekend is going to disappear with glider surveys and airworthiness reviews.


Thread: New Lathe - poor suface finish on my results
12/06/2020 11:30:24

The two most common causes of poor finish are the material and the tooling. So I'd make the following points:

Don't buy material from Ebay unless you know what you're doing and don't care about finish. The quality of material varies widely even for nominally the same specification. Proper EN1A is one of the more forgiving steels and should give a good finish.

HSS tooling should produce a good finish, but is dependent upon how it is ground. You do not need fancy guides and setups to grind HSS (I hand grind my tools) but the shape needs to be roughly correct with proper clearance.

Insert tooling can be fussier about cutting conditions. It's possible that a small lathe simply won't have the speed and power to get the best from inserts. The same caveat applies to inserts as to materials; cheap inserts may not perform as well as more expensive branded ones.

A stick out of 60/70mm without tailstock support is quite ambitious on a small lathe.

Recutting on the way back to the tailstock is normal, even on industrial lathes. It's due to work and tool deflection, and the cutting process itself. It will become second nature to simply withdraw the tool, wind back and reset the tool position.

For HSS tooling and 12mm diameter EN1A I'd be running at about 800rpm (100 feet per minute surface speed). For insert tooling you can easily be three or more times that.


Thread: R8 or morse taper 3?
12/06/2020 11:06:08

Posted by SillyOldDuffer on 12/06/2020 10:28:46

I'm not sure why R8 is rated in Europe.

Because there are a lot of Bridgeport mills, and clones, in Europe. Some real Bridgeports, including mine, were built in the UK. Tooling with R8 tapers has been available in the UK from commercial suppliers from long before the hobbyists started using it. Popularity is dictated by the commercial market not the home one.

Of course R8 is power limited, I think around 2hp is regarded as the maximum it can cope with. Another plus compared to Morse tapers is that it is, in theory, self-releasing, so no stuck tooling. It's a bit dinky, but it suffices on two of my mills. The third mill uses INT40 which is in a different league.


Thread: Parting off
12/06/2020 08:36:11

Not the same as turning but I've measured some chips created when milling with my new Arc face mills. In all cases the cutter was running at 900rpm and the feedrate was 430mm/min. With 5 inserts that gives a chip load of 0.096mm.

For aluminium (6082) I used a depth of cut of 5mm. The resultant chip measures 5.00mm wide and 0.35mm thick. It's interesting to note that the chip is tapered at one end. That implies that the chip gets thicker as the cut gets going and conditions stabilise.

For steel (hot rolled) I used a depth of cut of 4.5mm. The resultant chip measures 4.55mm wide and 0.19mm thick. The chip is also tapered at one end.


12/06/2020 08:22:29
Posted by David George 1 on 12/06/2020 07:11:26:

The forces on a tool when parting off have a different direction to turning and can be held better with a more solid rear toolpost.

Can you explain that please.


Thread: What Did You Do Today 2020
11/06/2020 22:16:42

This morning I did a grocery shop and delivery run for my mum.

This afternoon I made a new tie rod for the feed motor on the horizontal mill. Fortunately I had a 3/16" BSF die to hand. This evening I reassembled the motor and gearbox. Fixing the motor fan may have cured the problem, although the feed seems a bit noiser than I remember. We'll find out tomorrow when I recommence machining the cylinder. Out of interest here's a picture of the internals of the feed gearbox:


Seems logical; horizontal input shaft at the top and two sets of three gears to drive the lower shaft which then drives the vertical shaft via skew gears. That seems a bit odd as the drive must be transfered to the swivel point of the table to drive the leadscrew. It's many years since I've had the table off the mill so I can't remember the details.


Thread: Parting off
11/06/2020 08:03:48
Posted by Clive Foster on 10/06/2020 23:17:21:

Chips end up slightly thinner and slightly wider than the material was when on the parent bar.

Not sure I agree with that. For ductile materials at least, like low carbon steel, I think the chips are thicker than the feedrate might suggest and about the same width as the depth of cut.


Thread: What Did You Do Today 2020
10/06/2020 21:40:51

It was raining when I got up, equals double yippee. One, because the garden really, really needs it and two, because I can play in the workshop.

I decided to true up the second cylinder block. Having machined two surfaces square I started machining one of the faces perpendicular to the bores, with the casting slightly twisted to get the best alignment. I will true up the reference surface afterwards as there is still a lot of metal to remove from it. I was just starting the cuts with the second iteration of the twist when the power feed starting making intermittent noises. The immediate reaction was to ignore it. But if I do it'll only get worse, and there are no spares if something breaks. So I top up the gearbox from the motor to the feed gearbox - not much change. So next I fill up the feed gearbox, which due to poor design means I have to swivel the table (and lose my setup) to get to the filler. Do that and still not much change. The noise definitely sounds as if it is coming from the motor/gearbox. So take off the motor and gearbox combination:


A big gear on the feed gearbox input can just be seen to the left of the two levers that select the feedrate. It's a really messy job. Not only is the gearbox stripped, so was I as I don't want to get oil all over my decent shirt. On looking more closely I notice that the motor fan is loose as the bolt has unscrewed. The fan cover is removed and the fan is fixed. I ran the motor in this configuration and it "seemed" better. But annoyingly I damaged one of the rods holding the motor together. By the way the feed motor is 1hp.

The next tasks are to make a new rod, re-assemble the motor, refit the motor and gearbox and try it out. Then I might be able to get back to what I was doing.

At least the weather is going to be poor over the next few days. Which makes me glad I flew the big glider yesterday for a few hours of local soaring. It all went rather well given I haven't flown this glider for nine months. And I didn't make any boo-boos, which is a bonus.


Thread: Questions about lathe power feeds.
10/06/2020 09:30:19

This is the threading/feed plate from my M300:

threading and feed plate me.jpg

The gear train seems to be slightly different, although the last two gears also need to be reversed to get the coarser threads and feeds. The note bottom left clearly states facing is half sliding. Looking at the exploded diagram of the apron in the manual there is a 5 tooth low helix skew gear which might be involved in the feeds. That would be expensive to make. That could explain why import lathes use simpler alternatives, but leading to a higher ratio.

Some other points to make are:

In light of a recent thread on an odd 7mm and 1.1mm pitch thread it's interesting to note that 1.1mm pitch is listed.

In the manual the chart is extended to allow cutting DP and Mod worms using a 56 tooth gear in the drive train rather than 44 tooth.

My lathe is definitely power limited. With a decent cut I can hear the motor slowing as the cut comes on. I've pushed it far enough to stall the motor more than once. Calculations showed that I was trying to remove about 3 cubic inches of steel per minute. So the old rule of thumb is about right.


Thread: Cutting Oil
09/06/2020 09:24:24

Soluble and neat oils are different, and have different purposes. Soluble oils are intended to cool with a little lubrication, whereas neat oils are intended to lubricate with a little cooling.

With carbide tooling it's a moot point as to whether cutting fluid is needed. I don't use it for general turning and milling, except for parting off. I use soluble oil for drilling with HSS tools and on the horizontal mill with HSS cutters. I also use it on the CNC mill irrespective of tooling, mainly to wash away the swarf. Anything other than flood coolant is a waste of time, especially if the primary purpose is cooling.

Whether fluid is needed depends upon the chipping characteristics of the material. For long chipping materials, like steel, as the chip is sheared it is deflected (creating a pressure point) by the top of the tool before curling up and possibly breaking. The fluid helps to cool and lubricate the chip as it passes over the tool increasing the life of the tool. For short chipping materials, like brass and cast iron, the chips come off as individual particles so don't exert the same pressure across the top of the tool. In addition, for cast iron, swarf plus oil creates a sticky mess.


Thread: What Did You Do Today 2020
08/06/2020 22:04:15

Today I've been doing the initial machining on one of my traction engine cylinder blocks. I have three sides, the top and the width of the flange done:


All machining has been done on the horizontal mill with an 80mm diameter insert cutter. Here's a typical set up:


The biggest cut was 2mm deep, full width, 420rpm and 420mm/min feed, not even a hint that the mill noticed it. I love it! And just to stir up the old versus new debate the horizontal mill cost me £175. smile

The iron casting machined beautifully, but was all over the place in terms of dimensions and squareness. At least I've ended up with all the sides and top square to each other and to dimension (in my CAD model) apart from the two faces parallel to the bores which are 15 thou under. The width of the parallel faces on the unmachined casting varied from 5 thou over nominal to 150 thou over, so somewhat on the skew. It's annoying to be a bit under, but it's not a problem in practice. Although I might tweak some of the port dimensions on the liners at a later stage.

The angle plates in the picture were indicated to be parallel to the Y-axis before using them. Just as well I checked, as setting them perpendicular to the front of the table with a set square meant they were many thou out. Since my horizontal mill is a universal (the table swivels for making helical cuts) I also indicated the table parallel to the column in X at the start.

Tomorrow I plan to fly the glider, before the bad weather sets in for the end of the week and the weekend.


Thread: Parting off
08/06/2020 21:28:33

Feedrate is the key to parting off. On the centre lathe, with an insert parting blade, I never use less than 4 thou per rev power feed, Parting off is now, almost, a routine operation.

On the repetition lathe, with hand feed and a hand ground HSS steel blade, I've measured the chip thickness as between 8 and 10 thou.

To summarise; don't pussyfoot about!


Thread: A red face and a bottlejack
08/06/2020 15:14:02

Put it aside for another 35 years.


Thread: What Did You Do Today 2020
07/06/2020 21:03:34
Posted by JasonB on 07/06/2020 06:58:48:

That centre hollow section will be interesting to machine, look forward to seeing how you tackle that.

The answer is:


The access hole is 1/4" diameter.


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