Member postings for Andrew Johnston

Better not try 12.9 then!

What was the provenance of the bolt? My experience of buying import tooling is that the SHCS fitted are made of cheesium, but may be some of them are tougher than expected? I don't worry about shortening bolts with a hacksaw when required.

Andrew

Something wrong there. Here's the head of a 12.9 M12 bolt I just machined with a 5/16" square HSS knife tool that just happened to be lying next to the lathe:

Running at 540rpm with a feed of 4 thou/rev and DOC of 10 thou. The finish looks worse than it is real life. A few measurements gave an average surface finish of 1um Ra, which is about as good as I get when turning.

The tool sets from EB can go in the round filing cabinet. There are two rules for buying cutting tools:

1. Don't buy cheap cutting tools - applies to everything from files and hacksaw blades to coated carbide endmills

2. See rule 1

Perversely the rules apply even more to smaller lathes as they don't have the power and rigidity to overcome poorly ground or less than sharp tools.

In general I'd agree with JB regarding carbide inserts. They can create good finishes with small DOC, depending upon the material, but for carbon steels they prefer more like 10+ thou DOC and high surface speeds.

Andrew

I hope that applies to the OP as well; he has form for airily dismissing almost all attempts at help.

Andrew

Overall consumption seems high? I use about 2400kWh a year, a daily average of 6.5kWh. My background consumption, with most things off, is 60W. That's the mains powered doorbell, 3 DECT 'phones and TV and microwave on standby. I have 5 fluorescent tubes in my workshop. It was noticable how much power I was using, about 300W just having the lights on. The fluorescents were old and created a poor light so I changed to LED tubes nearly 2 years ago, followed by converting the rest of the house to LED. It's made a huge difference to my background electricity consumption in the workshop, down to less than 100W and the workshop is much brighter. But I still turn lights off when I leave the workshop, even for a few minutes.

Andrew

Not really, it needs to be more than an order of magnitude more sensitive, along with multiple graduations.

Andrew

Doesn't look like a precision level; I'd expect to see a number of graduations? What is it's sensitivity? For example on my engineers level one division equates to 0.0005" (half a thou) in 10".

Andrew

What sort of level? If you're going to use a level it needs to be an engineers precision level; DIY levels aren't even close.

There are methods of correcting tapers that don't need levels, but I'll leave those to others to explain as I've never needed to use them. To start with don't try and machine/measure with the tailstock in place. It simply creates two variables (bed and tailstock) to adjust but only one measurement. So it's doomed to failure.

Andrew

It's a box chuck, albeit larger than normal. Box chucks are standard accessories for clockmakers and instrument lathes.

Andrew

When they emigrate to the US.

Andrew

1. No idea

2. A machine reamer cuts on the leading chamfer, not the flutes, so essentially end cutting

Andrew

That's as maybe, but I have a Myford in the workshop:

Does that make me a hobbyist?

Andrew

To break HSS toolbits I grind a groove around the blank, put the blank in the vice covered with a cloth, and wallop it with a hammer. For more delicate stock removal HSS can be milled with carbide endmills.

Tool grinding is not complicated. Almost all my HSS tools are ground freehand with an aluminium oxide wheel. You don't need fences and fancy rests unless you need specific angles or shapes. The basic clearance and rake angles are non-critical and can be ground by hand. I don't worry about curvature on the clearance faces, although I also grind on the side of the wheel. That's lit the blue touch paper, now to retire to a safe distance!

Andrew

It's rather more complicated than that. My local tool emporium stocks metric reamers in 0.01mm increments. When I decided to buy a set of imperial reamers for my traction engine build I ended up with 4.76mm, 6.35mm, 7.94mm, 9.53mm and 1/2" reamers, by buying the cheapest in each (nominally imperial) size.

Andrew

Not so, you only need a means of indexing. It could be a rotary table or a plain dividing head. It doesn't need to be universal. You only need that for helical gears.

Andrew

To answer some of the OP's questions:

Yes, there can be significant disadvantages to using coolant. Some coatings, such as TiAlN, need to run hot (many hundreds of degrees) to work properly. Commercially it's a pain to have coolant being thrown around, and it decreases the value of the swarf.

Axminster is incorrect to say coolant is essential. All my manual vertical milling is done dry. I use flood coolant on the CNC mill, mainly to wash away swarf. Flood coolant is often used on the horizontal mill, as I mostly use HSS cutters and take heavy cuts (5hp motor).

There's no such thing as "solid carbide". Carbide tooling consists of tungsten carbide particles in a matrix of, usually, cobalt.

The Arc premium cutters are very good, but they're a waste of money on small mills as there's isn't enough motor power to make best use of them.

The finish when side milling is dependent upon chip load, not on the number of flutes. The profile on these parts was machined with a 2-flute ballnose cutter and a 3-flute square endmill:

I'd run a 3mm cutter in steel at 7500rpm for profiling and 6000rpm for slotting.

Soluble oils (water/oil) mix are primarily for cooling with some lubrication. Neat cutting oils are primarily for lubrication under high cutting pressures with little cooling. That's why neat cutting oils are often seen on gear cutting machines.

Andrew

An alternative to the rather neat rod method is to follow a template. Here's a smokebox door being machined using an automated (hydraulic) follower:

The template could just as easily be followed by hand manipulation of the slides. The method has the advantage of repeatability.

Andrew

I use the book on steam and heat engines by Ewing as one of my references when attempting to understand the underlying theory of steam engines. By the time my edition was published, 1926, he was Vice-chancellor of Edinburgh University.

Andrew

I'm beginning to suspect that the OP is actually the greatest gear expert who ever lived, and is just messing with us for his own amusement. But I'll do my best to answer the question for other forum members who might be interested.

A crown gear (aka a contrate gear) is simply a bevel gear where the pitch cone angle is 90 degrees. So they can be made with any of the methods used for bevel gears. In practice the face width of crown gear is small so the change in shape of the tooth form is very small and they can be satisfactorily cut, one tooth at a time, with an involute cutter.

There are two approximate methods for cutting bevel gears on a milling machine with involute cutters. One, the parallel depth method, uses standard involute cutters. The other produces tapered teeth in two dimensions rather than one, but needs special (narrow) involute cutters. Both methods require three passes around the gear. The second method creates gear teeth which lack curvature at the small end which needs correcting. I've never made bevel gears using the parallel depth method, but these test gears were cut using the second method 45+ years ago as part of my training:

No CNC used, all manual machines.

The first bevel gear planers were introduced in the 19th century by Gleason in the US. They used two reciprocating rack like cutters to form each tooth. Early machines followed templates but later machines eliminated the need for the template. If the OP thinks cutting one tooth at a time is slow he should watch a video of a bevel gear planer! I've not used one, but have seen one in action. Apparently they're difficult to set up and are temperamental.

Straight tooth bevel gears fell out of fashion to some extent, being replaced by spiral and hypoid bevel gears, which can be (approximately) cut using vertical rack like inserts in a circular holder. It's a much faster operation than planing. More recently Gleason have introduced the Coniflex straight tooth bevel gear. These can be cut with one, or two, circular discs with radial inserted teeth that form the teeth. They are much faster than the bevel gear planers, and presumably less temperamental as they are, of course, CNC.

Andrew

Never mind gas, it smells more like bullsit.

If we assume a coefficient of expansion of 10x10^-6 per degree C for steel then for a 10m diameter gear the diameter could change by 10x10x10^6 for one degree C, that's 100 microns. So there would be little point in measuring to microns. Alternatively, one would need to hold the temperature to one hundredth of a degree C, or less, for micron resolution to be useful. That's better temperature control than national standards laboratories.

With the involute system it's the shape of the tooth that is important, small variations in centre to centre distance are less critical, and don't affect the smooth meshing. So there wouldn't be any need to measure across a 10m diameter gear to microns.

Andrew

This very question has been answered recently on TractionTalk. Here's the link:

Tundish

I think one needs to be a member of TT to view pages.

Andrew