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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: 9/32 hex steel bar
02/09/2021 10:58:12
Posted by malcolm conomy on 02/09/2021 10:48:05:

more like 3000

I was going to say make your own 9/32" hex by milling from round but not practical for 30m.

I'd use 7mm hex - hope you've got a decent repetition, capstan or CNC lathe.

Andrew

Thread: Cleaning my lathe
02/09/2021 10:52:42

Old paint brush plus dustpan and brush and kitchen towels. In the drip tray i have a rectangle of steel sheet for moving swarf around the drip tray, and over the edge into a bucket. There's also an old hacksaw blade for moving swarf from awkward places.

I aim to remove swarf and excess oil - not the slightest bit interested in the lathe looking pristine.

Andrew

Thread: 5 Rotary Table/Tailstock/Chuck Kit Info/Questions
01/09/2021 21:31:40

When I bought my (secondhand) rotary table I also bought a small import 3-jaw chuck. I've never fitted it and not missed it, so I never will fit it. I mount work direct on the table.

Andrew

Thread: Is there such a thing as an 'external reamer'?
01/09/2021 09:37:33

A UK supplier, although still not cheap:

Hollow End Mill

Andrew

Thread: Scribing with verniers
31/08/2021 16:45:12

Wow, scribing lines? That really is old school. smile

I very rarely mark out now; mainly for sheet metal that will be filed/drilled by hand, and for the odd reference point to aid setting up a casting. I use a secondhand mechanical vernier height gauge and surface plate and very rarely odd legs; never used my vernier calipers. But then again I rarely use my calipers as I prefer micrometers.

Andrew

Thread: Mounting stuff to a Faceplate
30/08/2021 22:13:42
Posted by Nick Welburn on 30/08/2021 20:47:15:

Is it the done thing to drill and tap the face plate..............

Definitely not, large faceplates are not cheap! I use existing slots, but if needed I'll make a smaller plate, or block, to hold the part:

teper plug reaming.jpg

Andrew

30/08/2021 20:39:28
Posted by Nick Welburn on 30/08/2021 20:01:28:

Do I just use t nuts and my wedge things with the little serrated triangles? This looks like a dangerous option for launching metal at speed.

Nothing wrong with normal clamps and blocks, or anything else for that matter, provided the setup is thought through in terms of what might move under cutting forces. You'll not be running fast, no more than low hundreds of rpm. Here are some examples:

flywheel_setup.jpg

water pump bypass spigot.jpg

smokebox_turning.jpg

Andrew

Thread: Traction engine build
30/08/2021 19:55:32

Welcome to the forum. thumbs up

I assume you mean Live Steam Models aka LSM? I'll start by stating that whatever advice I offer it is inevitable that somebody will pop up to say they made a 6" scale engine on a mini lathe. teeth 2

A Boxford is on the small side for a 4" scale traction engine. There will be a substantial number of parts which simply cannot be machined on it. I have a 13"x40" lathe which will swing 18" in the gap. That is sufficient for all the turned parts on a 4" scale Burrell SCC. While it is possible mill on the lathe again there will be a substantial number of parts that are too big for a Boxford. For milling I have Bridgeport vertical mill which is sufficient for most parts. While gears can be cut on the Bridgeport I have a large, but cheap, horizontal mill which greatly eases the cutting of the 5DP and 6DP gears needed and also doubles as a cheap horizontal borer.

Before building my engines I bought the plans, worked out what the largest diameter and longest parts were, and chose a lathe accordingly. The mill is less critical but the bigger the better, as bigger has more rigidity and a greater metal removal rate. A look at my photo albums will illustrate the nature of the tasks that need to be done. As a caveat I like to make all parts myself rather than buy in when required. So far the only big jobs done professionally have been the boilers and vulcanised rubber tyres.

Andrew

Thread: Coolant pump - how to slow flow rate?
29/08/2021 20:04:24

Interesting; most of my coolant pumps, 3-phase industrial and single phase home brew, simply have a tap on the output to regulate flow. Ironically the only pump that failed (motor winding short) was the 3-phase OEM pump on the Bridgeport, which didn't have an output tap.

Andrew

29/08/2021 08:36:00

Put a clamp on the hose or fit a valve in the hose.

Andrew

Edited By Andrew Johnston on 29/08/2021 08:36:38

Thread: A SIMPLE POINT !
27/08/2021 10:53:33

Set screw is the correct technical term. But unfortunately sloppy definitions mean that set screw can also be used to mean a grub screw. Machine screws imply a non-hexagon head.

It's almost as bad as describing a milling machine as universal just because it has horizontal/vertical capability.

Andrew

Thread: Mill vise and rotary table
25/08/2021 11:43:23

Another consideration is that having a heavy item at one end of the table makes it much harder work to wind the handles, in all axes.

Andrew

25/08/2021 09:49:01

I find having multiple items on the table never seems practical, something always seems to be in the way. So I generally fit just the item I need to use; my mill table is 48" long.

Andrew

Thread: Getting accuracy with my newly added DRO.
23/08/2021 21:26:34

I'm not sure what the problem is? Edge finding and cutter diameter are separate issues. All my standard carbide cutters are on size, or a maximum of 0.01mm under, on the shanks. For general work I never worry about the cutter diameter not being as stated. if i use old HSS cutters, or a slot or edge distance needs to be accurate (say better than 1 thou) then I'll cut 'n' measure using depth micrometers or gauge blocks and adjust as needed.

In all the years of using a CNC mill I've never used cutter compensation. Parts fit together straight off the mill. Occasionally I'll tweak the CAM program to cut under, or over, by a small amount as required.

Andrew

Thread: cutting spur gears on a mill
23/08/2021 21:02:17
Posted by JasonB on 23/08/2021 20:45:40:

....they are likely to make better hobs than a standard tap.....

Specifically spiral flute, as opposed to spiral point.

Andrew

Thread: Is there such a thing as an 'external reamer'?
23/08/2021 10:12:00
Posted by John Reese on 23/08/2021 00:42:22:

For a dozen parts special tooling cannot be justified.

Oh dear, I've been making special tooling for onesies and twosies:

cutting tools.jpg

embarrassed

Andrew

Thread: cutting spur gears on a mill
20/08/2021 08:48:17
Posted by Martin Connelly on 20/08/2021 08:36:56:
Anyone who has ever cut gears will know that there is great satisfaction in it............

final drive gears fitted.jpg

worms and worm gears.jpg

Cast Iron Gears

governor bevel gears me.jpg

skew gears.jpg

Must be careful not to get over-excited. teeth 2

Andrew

20/08/2021 08:35:20
Posted by Nathan Sharpe on 19/08/2021 22:39:29:

If I were to use the same tap to cut a number of gears with varying diameter with the same tap would they mesh or would they not? Yes, they should do, although I've never tried it.

If I were to introduce a "worm" of same thread between gears would I be able to build a gear train to increase/decrease speed? Yes, the worm wheel I showed being made with a tap mates smoothly with a screwcut length of 7/16" UNF thread. However, it will only decrease speed. The worm wheel will not back drive the worm unless the helix angle of the 'thread' is much larger.

I've never cut a gear in my life so have no idea, would like to know where to start If I wish to! Making a non-critical worm drive is fine using a tap. For spur gears I wouldn't start here.

See answers embedded above.

Andrew

20/08/2021 08:07:55
Posted by Martin Connelly on 19/08/2021 22:16:26:

The spiral path goes along the rotating tap regardless of the angle so there will be a pressure on the blank from the tap whether angled or not.

Ooops, I think you're correct. embarrassed

However, that raises a question; if the tap/hob can drive the work why do hobbing machines go to the trouble of actively driving the gear blank?

Andrew

19/08/2021 21:32:47
Posted by brian jones 11 on 19/08/2021 16:37:38:
I belong to the school of thinking first and asking around before making chips.........

Unfortunately you seem to have mislaid the first step. If the tap is skewed by the helix angle to get straight teeth on the gear how does it drive the gear blank as there will be no tangential force. The tap drives a worm wheel because it creates teeth that are not straight and hence there is a force causing the blank to rotate.

Andrew

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