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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: Reducing shank diameter on a reamer.
20/07/2018 22:41:29

I'm no expert, but I agree with NDIY.

Let's assume we can reduce the shank on the reamer, but to what concentricity, say 1 thou? If we're lucky the 3-jaw chuck may hold concentric to 1 thou, but may be a whole lot worse. So that's the "cut" gone before we start. Given that the reamer has a parallel shank we can assume it is a machine reamer. Like all tools reamers need to cut, not rub. A 2 thou cut is rubbing. For a 16mm reamer I would leave a 0.3-0.5mm allowance for reaming.

If it is essential to remove 2 thou from the bore I'd dial in the bush in a 4-jaw chuck and then take a fine cut with a boring bar,

Andrew

Thread: Aircraft General Discussion
20/07/2018 17:06:00
Posted by martin perman on 18/07/2018 17:18:32:

...............and over the house came a very low, 500ft, DC 6 heading in the direction of Coventry. I assume it was Air Atlantique's. What a sight.

Ah, the penny drops! When I was flying the small glider near Gransden Lodge on Monday afternoon I say what was clearly a multi-engine prop driven aircraft heading towards Cambridge. It was clearly a vintage aeroplane, but I wasn't sure what. Now I've looked up DC6 that is definitely what it was; the tail is identical, an angular fin and rudder with a narrow chord.

Andrew

Thread: Internal thread cutting (the basics)
20/07/2018 15:41:39

Hmmmm, according to my tables the OD of a 5/8" BSP thread is 0.902". So if you want to cut a matching internal thread the ID to start with needs to be the OD of the external thread minus twice the thread depth, which I make 0.811".

I've never tried cutting a RH thread with the tool moving away from the headstock, but it is possible. Now that I've got a high speed threading unit, with auto trip, I don't bother to make an undercut. I just let the cutter make its own. For standard threads I tend to use threading inserts, so don't bother setting the topslide over by half the thread angle. Apart from anything else it messes up the trip position. This is screwcutting 3/8" BSP threads, at 280rpm and three passes plus a clean up pass for less than a minute per thread:

screwcutting_bsp_me.jpg

Andrew

Thread: Arbor Press Question
18/07/2018 17:47:38
Posted by Richard Harris 5 on 18/07/2018 17:28:14:

Any idea how heavy these are? Wondering if two people can lift it into a van or not...

I would think well into the hundreds of kilos, depends upon the people of course, may be ok if you've got Geoff Capes available. As I recall two of us couldn't lift a #3 into a hatchback.

Incidentally I understand that the number refers to the tonnage that the press can exert. Anybody know if this is correct?

Andrew

Thread: Bridgport Nut
18/07/2018 14:52:33

Just had a closer look at mine. It's not a nut as such. More of a threaded bush that fits in the yoke and is stopped from rotating by a dowel in the smaller hole shown.

Andrew

18/07/2018 14:19:23

Don't have time to check mine with a tap at the moment, but if it's 14tpi it'll be 7/8" UNF as 7/8" BSF is 11tpi.

Andrew

Thread: M300 Suds Pump with inverter
18/07/2018 11:43:16

I'm beginning to think that the coolant pump may be fudged? If it won't run in star or delta it probably is.

I can't remember where I got my replacement 3-phase suds pump for the Bridgeport, as well as a single phase one for the CNC mill, but there are plenty of industrial suppliers out there. I had a bit of a to do with the single phase pump. Naturally I ordered a 240V version. When it came to wiring up it said 110V inside the connection box. So I called the supplier, who was rather rude and implied I knew nowt about electrics. I persisted and eventually they checked their stock. Turns out they'd ordered a batch of 240V units, and the units had a 240V sticker on the outside, but were really 110V units inside. Wonder how much that cost them in warranty claims! At least they apologised for being rude.

Andrew

Thread: How much space do I need for a seig sx2.7 mill.
18/07/2018 11:32:21

When I first installed my vertical mill, in a corner, I checked out the positioning using a graph paper cutout on a scaled drawing of the workshop. Helpfully the manual includes a proper plan drawing of the mill showing the extremes of travel of the table, and ram, including the handles. The travels are tabulated according to table size and power feed or not. So it's easy to work everything out without needing to measure.

I've subsequently removed the lefthand handle, for three reasons:

1. When using power feed I don't want the handle catching me in a painful place, or hitting other machines

2. It gives me a bit more space

3. I use the lefthand end of the leadscrew to drive a dividing head for spiral milling

Andrew

Thread: Lathework for Beginners
18/07/2018 09:59:32
Posted by Ron Laden on 18/07/2018 09:00:58:

I was going to print one off and mount it above the lathe as a beginners guide when I wondered is there a chart you guys would recommend

On the whole I don't bother with charts. The speeds are mostly not that critical within a few percent. And finish is also determined by a host of other parameters including depth of cut, feedrate, quality of tooling, rigidity of the machine and the material itself. I've got the basic numbers in my head and if needs be I do a quick mental calculation and that gets me close enough. In the end it's experience that counts and you only get that by experimenting.

Andrew

Thread: What did you do Today 2018
17/07/2018 22:05:42

Given the number of subjects we're not supposed to discuss by neccessity this will be a truncated report. wink 2

This morning I drilled and counterbored all the holes for holding the perch bracket castings to the smokeboxs on my traction engines. Then I measured the thickness of the castings at each hole to assess the range. I've sketched out a stud for the thickest hole. After I've made all the studs the same I'll adapt each of the others during fitting so I have the same amount of thread showing for each one.

As well as the studs I need to make some more nuts, washers and bolts for fitting castings to the smokebox. At the moment the repetition lathe is set up for shortening rivets for the rear wheels. Rather than break down and have to set up again I decided to shorten all the rivets I will need for the remaining two rear wheels. Turned the power on, hit the start button, one second delay and flash! What the *&@! Obviously an electical event, down near where my 3-phase extension lead connects to the machine plug. No trips on the distribution board. So I tested the socket using the pillar drill - all fine. Try running the pillar drill via the extension cable - nothing. Obviously the cable is fudged. I took the socket apart at the end where the flash occurred. All looked fine, no loose or broken wires. Working back from the socket I found broken insulation and burnt wires about 15" from the socket. I suspect the cable must have been trapped and damaged at some point. It took about 10 minutes to cut back and rewire. Tested it on the pillar drill and all working again.

So back to the task in hand, shortening rivets. I really got into the swing and shortened the full complement of 150 rivets in 45 minutes. All I need to do now is finish building the wheels so I can use the rivets.

Andrew

Thread: M300 Suds Pump with inverter
17/07/2018 19:05:45

Something doesn't add up here. The coolant pump plate clearly indicates that the motor is dual voltage. The manual I have for my M300 gives exactly the same part number for the coolant pump (AQ3/2/Q) for both the 415V UK and the 220/380V European version. Which implies that the coolant pump can be reconfigured.

The company M G Electric are still going, selling the AQ4 version now. Might be worth asking their technical group about the AQ3.

I'd also go with the suggestion from Ian, try it configured as star, it ought to run on 230V. If not the motor is probably badgered.

Andrew

Thread: Lathework for Beginners
16/07/2018 19:16:53
Posted by SillyOldDuffer on 16/07/2018 13:38:20:

Not cut Nylon myself. I'd guess high-speed with a sharp knife-like tool.

................

Perhaps someone who has done it will advise please?

In all cases it's the material that initially gets hot due to deformation as a result of chip formation. The problem with plastics is that they go soft, and even melt, at low temperatures. And you don't really want to be using flood coolant, as many plastics will absorb it to some extent.

The trick to machining plastics is sharp tooling with high rake angles, and uncoated, and ideally polished, if using carbide. Superficially one would think high speeds would be great for plastic, but in reality slow speeds are needed to prevent melting, say low carbon steel/HSS type speeds. To compensate large DOC and feedrates can be used, say 10 to 20 thou per rev or per tooth.

Nylon machines well, but it's near darn impossible to get the swarf to break. So you end up with an ever increasing ball of swarf that would put a birds nest to shame. The best thing is to stop and remove the ball of swarf at regular intervals. If it gets caught up the results can be spectacular. If the ball of swarf rubs on the work it can get hot enough to melt, equals a right mess.

To summarise, cut slow with high DOC and feeds.

Andrew

Thread: Arbor Press Question
16/07/2018 10:02:46

The hole in the ram on my flypress is plain 1" diameter with an external screwlock.

For bending fixtures I use hot rolled steel. Similarly for riveting/shearing/punching I use hot rolled steel for the fixture but make the tooling from silver steel or gauge plate properly hardened and tempered.

Andrew

Thread: Political views within the forums
16/07/2018 09:55:59
Posted by Michael Gilligan on 16/07/2018 08:51:11:

Think of it as a midden ... It's serving to keep the rubbish in one place.

Quite a bit of what is posted on the forum falls into that category, not just what is in this thread. smile

Andrew

Thread: How to machine an ellipse
15/07/2018 21:22:17
Posted by John Haine on 15/07/2018 20:39:27:

Generating an elliptical outline or hole in a plate is trivial using CNC

Like the cutout in the centre of this spacer, just for the hell of it:

water pump spacer.jpg

Andrew

Thread: milling qestion
13/07/2018 22:17:30
Posted by Tim Stevens on 13/07/2018 20:31:22:

If your mill is a hobby type (not a solid heavy duty industrial model) then it is likely that a slot drill will be pulled over as it cuts*, so the edge of the slot isn't quite where you hoped.

I've never used a hobby type mill, but I don't see why a slotdrill should cut wide on one. When the cutting edge reaches the widest point the edge will rub to start with, and the cutting edge will tend to be pushed away from the widest point of the slot. As the edge continues to rotate eventually the edge will start to cut instead of rub. But at that point the edge will be past the maximum sideways excursion, so even if it tends to pull the cutter towards the existing edge it won't cut wide.

Now I grant you I have a Bridgeport, but that isn't the most rigid of machines, and it's well worn. But slots cut full depth in one pass are within a thou on width, as measured with gauge blocks. At least some of that error is due to tolerances on the cutter itself.

Andrew

Thread: How can I drill a deep, non-standard, small diameter, hole?
13/07/2018 19:47:57

I've drilled down to 1/32", in brass, on my lathe. But TBH I don't like the combination of small drills and large lathes. It's difficult to get the drill started. Spot drills are better than centre drills, but not perfect. And the small drills, although held in a pin chuck, have a tendency to wander. Must get the Pultra up and running, 6000rpm and a lever tailstock should be better!

Using smallish drills on the Bridgeport is much easier. I've drilled a load of 0.7mm holes 10mm deep in brass without a problem. I didn't bother with spotting first. Just a light touch enables the drill to make it's own mark and then one can drill normally. The modus operandi is to peck frequently, every few drill diameters, and to make the drill work. Even for small drills the feedrates can be surprisingly high. With slightly larger drills I've successfully drilled 1.2mm holes 10mm deep. Normally that would be yawn territory but it was in a tungsten alloy with a slow helix carbide drill.

To summarise, bin the lathe and try the vertical mill.

Andrew

Postscript: I was recently given a high speed (10000rpm) PCB drilling machine which I shall be using in future for small holes. thumbs up

Thread: milling qestion
13/07/2018 15:32:39

I'd mark out the ends of slot using traditional techniques and the drill all the way through using the mill. Change to a slotdrill and mill the slot to full depth, stopping slightly short of the ends of the slot. On the last pass I'd take the slotdrill to the ends.

With any cutter, irrespective of the number of flutes, as long as you're cutting a full width slot it makes no difference which way you feed. So yes, you can mill in both directions.

Andrew

Thread: How can I drill a deep, non-standard, small diameter, hole?
12/07/2018 17:29:15
Posted by SillyOldDuffer on 12/07/2018 17:19:11:

Making fine drills in a home workshop must be possible, any ideas?

Stop messing about and buy one! Drill Service have a range of 0.3mm twist drills to suit all budgets.

Andrew

Thread: Any tips for Machining (turning down) a Hardened (60c) shaft on a Myford 7
12/07/2018 08:02:13

It's perfectly possible to turn hardened steel with ordinary CCMT style inserts, but for best results I'd agree with Mark and go for CBN inserts. Just sit down before looking at prices.

The posts in this thread on turning hardened silver steel may be of interest:

**LINK**

Andrew

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