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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: drillling bronze
15/09/2019 21:17:08

Although bronze, and gunmetal, can snatch like brass, generally I don't have a problem with drills less than 6mm or so. However, I run industrial machines. Even if the smaller drills do snatch they're not capable of pulling the tailstock along for instance. Larger drills are a different story; they can simply pull the Morse taper out. One can go up in small, say 1mm increments, but that can get tedious. I have used the slot drill trick, sometimes it works well and sometimes not; it depends upon the helix angle of the cutter.

Stoning the cutting edge has never worked for me; possibly I'm too aggresive on feedrates. Instead I've bought a small selection of slow helix drills from about 1/4" to 1/2". Above that I prefer to use a boring bar.

I haven't really noticed bronze closing up after drilling, but have definitely seen it when reaming. After reaming bronze (with a machine reamer) the reamer will not re- fit in the hole by hand. When I was grinding the rams for the water pumps on my traction engines, to fit the existing reamed bore, I had to go about 3 tenths undersize to get them to fit. So either my 17mm reamer is fudged or the gunmetal casting had closed slightly.

Assuming the thread is M3 a 2.5mm drill is slightly on the small size. I'd be using 2.7mm on bronze.


Edited By Andrew Johnston on 15/09/2019 21:18:51

Thread: Mill bit for cutting HSS
15/09/2019 20:55:29

Any carbide milling cutter will work fine in HSS. Here's an involute shape milled on the end of a 1/4" HSS toolbit prior to using it to cut an internal gear:

embryo cutter.jpg

The cutter is a 3 flute uncoated carbide slotdrill. Similar to turning hardened steel use reasonably high surface speeds, shallow DOC and high feedrate. Ideally the shear zone should be red hot as that will soften the steel where it is being cut, but leave the bulk of the material hard.


Thread: Spiral Flute Tap?
15/09/2019 08:39:39

That's interesting; I've never seen spiral flute taps described as anything other than spiral flute. Definitely no options have been listed. I've always tapped both through and blind holes with one tap only. Where are the different types of spiral flute tap advertised?


Thread: Black Bar
14/09/2019 12:07:12

EN3 is the most common spec, but not the only one. You can get EN8 as black bar.


Thread: Spiral Flute Tap?
14/09/2019 09:56:34

They're described as machine taps as that is how industry uses them. The hobbyist market for them is insignificant. Of course that doesn't preclude their use as hand taps in the hobbyist community, but it's not how the main market uses them. In the same way you can use ordinary hand taps under power in a machine, but it's not how they're generally used.


14/09/2019 00:00:03

Spiral flute and spiral point taps are intended for machine use, and the important feature is that the swarf is controlled. A spiral point tap has straight, angled, cutting edges that push the swarf ahead of the tap, ideal for through holes. A spiral flute tap actually has spiral flutes, which push the swarf back and out of the hole. In a ductile material the swarf tails can be inches long.

To re-iterate both types can easily be used for hand tapping. I find it ok starting spiral flute taps by hand up to about M6. Above that it gets more difficult. A spiral flute tap only cuts on the first thread or two, so is as good, or better, than a bottoming tap for threading depth in a blind hole.

While I often use spiral flute taps by hand they really come into their own under power. With the right tapping heads they can be run fast. I run from 500rpm to over a 1000rpm on my manual machines. It's way quicker tapping the hole than drilling it in the first place.


Edited By Andrew Johnston on 14/09/2019 00:01:38

Thread: THIN cutting oil - Suds alternative?
12/09/2019 10:02:57

On my (rarely used) drill press and vertical mill I drill dry with one exception. On aluminium alloys I use a quick spray of WD40 to prevent the swarf from sticking to the tool. Nothing to do with cooling or lubrication.

On my lathes I use flood coolant when drilling with HSS drills, except for cast iron, brass and plastics. I run drills fairly hard and flood coolant is built into the machines so I use it.

For coolant I use Castrol Hysol XF, a multipurpose soluble oil. I use it for some turning, horizontal and CNC (but not vertical) milling and grinding. I don't care about staining, although it's not an issue. Rust simply isn't a problem, provided you keep the concentration in the correct range. As the water evaporates it leaves a film of oil. I don't understand how wear comes into it? Nasty niffs are reputed to be a problem with soluble oils. I've never had a problem even though the coolant sits in the tank for months, or years, being topped up as required.


Edited By Andrew Johnston on 12/09/2019 10:04:41

Thread: Why are insert toolholders so expensive?
10/09/2019 21:10:57

Several reasons, first the quality of material and heat treatment. These are needed as the tooling may be in use for many hours a day over a long period. Industrial users will most likely be using higher speeds, DOC and feedrates than a hobby machine can, so the forces on the tool holder will be much higher.The toolholder needs to be stiff, you don't want it bending under the high cutting forces. Also the precision to which the toolholder is made is critical. When an industrial user swaps an insert it is expected to go back into precisely the same place and wothout any shake so that position references and tool height do not need adjusting.


Thread: Loco wheels cast iron grade ?
10/09/2019 09:35:49

Who'd have thought so little could generate so much! Must remember to attach a detailed glossary to future posts.


10/09/2019 09:00:16
Posted by JasonB on 10/09/2019 07:12:55:

.............unless you are able to resort to a cylindrical grinder.

That would have been the preferred option, but my cylindrical grinder is only 12" between centres. sad


09/09/2019 21:04:41

Wot, no splines? smile

Both my crankshaft and front axle are long 'n' thin. So definitely a candidate for chatter. But when it happened it proved difficult to get rid of. Eventually cured it by forcing a block wood against the work piece to add damping. It also explains why the diameter of the eccentric side of my crankshaft is different on the two crankshafts. embarrassed


09/09/2019 19:25:51

Cast iron is strong in compression but relatively weak in tension. And it is not ductile, so wouldn't stand up to the hammering from the track and out of balance forces. In contract SG iron is processed so that it is good in tension and compression. As examples both the front axles and crankshafts on my traction engines are SG iron castings. It's a PITA to machine as it chatters more than an Islington lovie. Cue a response from Jason saying it's no problem. smile However, for disc wheels steel will be even better, probably cheaper and less messy to machine.

Full size spoked wheels consisted of a cast iron centre with a shrunk on steel tire. The steel tire had good wear and shock load capabilities and being shrunk on put the cast iron centre in compression.


Thread: Recommendation for Tool and Cutter Grinder
09/09/2019 14:34:13
Posted by Chris Gallagher 1 on 09/09/2019 14:26:01:

The screws are from M1.2 to M0.9. Will a milling cutter cut HSS?

Yes, although it needs to be carbide. Here's an involute shape milled on the end of a piece of 1/4" square HSS for use in cutting an internal gear:

embryo cutter.jpg

Excess material and relief was added by hand on a bench grinder prior to use.


09/09/2019 14:19:11

Ah, that's easy. Just one pass with a milling cutter leaving an outstanding rectangle on the left edge of the tool. Presumably the width and depth of the rectangle don't need to be large. No need for a grinder. Have you looked at the tooling mentioned by Jason? What constitutes a small screw? I normally just lightly countersink the mating part, but I rarely deal with anything much less than M3/6BA.


09/09/2019 14:02:08

But that would give a rather rough finish on the flat face, dependent upon the number of passes and infeed increment. Given that the flat face is the important one it would seem sensible to make sure it is smooth and perpendicular to the rotational axis while being less worried about the angled face.

I suppose we'll have to wait and see if the OP enlightens us as to what he is hoping to do.


09/09/2019 13:28:47

Don't see how that works? The toolbit as drawn has an internal acute angle on the left, but a buttress thread is simply a lop-sided Acme thread where both angles are obtuse.


Thread: How to upset the neighbours!
09/09/2019 11:31:22

Lola, now there's a name from the past. Just up the road from Pi Research, although we didn't have a lot to do with them. A lot of the Indy car work we did was with Penske, who were unusual in designing and building their own chassis.


09/09/2019 10:52:37
Posted by JasonB on 09/09/2019 09:25:35:

Looks like Airoquip fuel line rather than nitrous hoses to me.

That's disappointingly normal. sad


Thread: Recommendation for Tool and Cutter Grinder
09/09/2019 10:50:30

That shape would be a challenge, and I don't think the grinders illustrated are in any way suitable. A better solution would be a surface grinder, or a T&C grinder like a Clarkson, plus a universal vice and a way of wheel dressing fancy shapes. Altermatively mill the shape.

It's all moot as I agree with John in that the first cut in metal will probably result in the tip going ping. If the width at the top of shape is 0.35mm then the base must be less than 0.2mm, along with a sharp corner as a stress raiser. If the shape was a rectangle and cuts were straight plunges you might get away with it. Easier to make as well; I'd use a mill.


Thread: How to upset the neighbours!
09/09/2019 09:06:09

Errr, it's a car. smile

With what looks like a straight six engine and nitrous oxide injection?


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