Member postings for Andrew Johnston

Hmmmm, if I've got my calculations right, and assuming the journal is 2" wide, I make that a difference of 0.000083" on the radius. In other words less than a 10th of a thou. The tolerance variation would be rather smaller.

Under wartime pressures to get engines off the production line I suspect it may have been quietly ignored, plus a certain amount of muttering by machinists about draughtsmen who came up with the tolerance in the first place.

Regards,

Andrew

Tolerancing didn't do W. H. Allens any good; the factory is now a housing estate.

What's left of the company is camped out in what used to be A Block of the grammer school in Bedford wot I went to, before it closed. Come to think of it, all of the schools I went to in Bedford have been closed and/or knocked down. Hmmm, may be there's a pattern there?

Regards,

Andrew

Ian,

Perfectly possible; here's a picture of the rear wheel rims for my traction engines being machined to width in stages:

The rims are a bit over 6 feet in length, while the milling machine table is 4 foot, with 790mm of travel. I also machined a V-groove down the middle of each rim using the same clamp and shift routine.

I have machined parts on my CNC mill that exceed the table travels. With careful jig design, tool setting and attention to cleanliness, ie, no trapped swarf, it was possible to achieve sizes appropriate to the accuracy of my machine, about ±0.03mm.

Of course, as we all know, bigger is better, but that will depend upon budget and space.

Regards,

Andrew

Personally I find that rather an insulting post; one might almost think that the poster was an obscurantist himself.

Andrew

Totally different; it's not a tool steel for a start, as it contains no iron. See here:

**LINK**

Regards,

Andrew

Olly,

No problem; as to why you'd want a collet alignment screw I don't know. On my secondhand vertical mill (varispeed head Bridgeport) the screw had been sheared off before I bought the mill. I've never bothered to replace the screw, and haven't missed it.

Regards,

Andrew

Sorry, but the small screw in a R8 taper spindle is not a drive key, it is purely for collet alignment. The torque is transferred through friction on the R8 taper. This is not a self-locking taper, so the drawbar needs to be fairly tight, otherwise the small screw gets sheared off.

Steve,

Just to clarify, the spindle taper would be MT2, MT3 or R8. With any of these you can then use finger collets, which are limited to one nominal size per collet. Alternatively you can fit an ER collet chuck in whichever taper you have, which uses a range of collapsible collets, each one of which covers a smaller range, usually 1mm.

Personally I'd go for a R8 taper in the spindle, as it is still used industrially so there is a wide range of tooling available across all price/quality bands. I use an ER20 collet chuck for a lot of my vertical milling. I can't say that I miss the upper range of the larger ER series, although I do have an Autolock style chuck if needed.

Regards,

Andrew

Nothing to add to Jason's advice. The designation CCMT is the first part of the ISO description of tool inserts:

C - Rhombic shape, 80º nose angle

C - Relief angle 7º

M - Tolerances ±0.013mm

T - Single sided, partly cylindrical hole, with a 60º countersink, ie, held by a central screw

Following numbers describe the size of the insert, the nose radius, the thickness and more. By far and away the most common insert, sold by most distributors, professional and ME.

Regards,

Andrew

Edited By Andrew Johnston on 13/01/2013 20:49:33

Neil,

Thanks for the information. In electric motors (DC and AC) it is common to have winding temperature ratings in the order of 100-200ºC. Granted in a DC brushed motor, with rotating coils, the cooling is less effective than an induction motor where the coils are static, but the case can still get pretty hot without a problem.

I suppose what I was really trying to say is there actually a problem, or is the OP just being understandable cautious?

Regards,

Andrew

I agree, but the OP mentions a mini-lathe so presumably it doesn't have a back gear; as the motor speed is reduced the torque doesn't increase. Consequently the power available decreases in proportion to the speed reduction.

The answer is to run as fast as you feel able to do so, to maximise the power available, as suggested by Neil.

Regards,

Andrew

The motor getting hot may not be a problem. Certainly induction motors are designed to run hot when operating at full load. Hot means you will burn yourself if you touch the motor casing.

Regards,

Andrew

You can get a keyed drill chuck to grip more tightly by going round each hole with the key in turn, rather than just using one hole to tighten the chuck.

Regards,

Andrew

Well spotted Neil - Andrew

It's roughly right, but not the whole story.

The density of iron is about 7850kg/m^3, aluminium is about 2710kg/m^3, so as correctly stated aluminium is about a third as dense as steel.

A typical tensile strength for EN1A is 400MPa, for pure aluminium (1050) about 130MPa, depending upon temper. So pure aluminium is only a third of the strength of EN1A. However, pure aluminium (1050) is unlikely to be available in any form other than sheet, as it bends easily without cracking, but machines badly.

The inners of the wheels would most likely be made from an aluminium alloy. For a common aluminium alloy, 6082, with a mid-temper, tensile strength is around 260MPa, so more like two thirds the strength of steel. For an aircraft spec aluminium alloy, 7075 with a T6 temper, tensile strength is around 500MPa, so stronger than steel. If it wasn't then we'd make aeroplanes from steel as it would be cheaper.

Regards,

Andrew

Raymond,

Thanks for the results on EN24T, looks like an excellent finish was obtained. I assume that DOC and feedrate are in mm, pretty impressive if not?

Regards,

Andrew

Errrr, I make 12tpi to be 83.3 thou per turn?

Regards,

Andrew

I have the following drill sets:

Numbers 1-60: at least 40 years old, no idea of manufacturer, possibly Presto?

Numbers 61-80: also old, no idea of manufacturer

Blacksmiths metric drills: from Chronos, nothing to write home about, but sometimes useful on the vertical mill when headroom is an issue

Letter drills: Dormer, conventionally ground

Imperial 1/16" to 1/2" by 64ths: Dormer, conventionally ground

Metric: 1-6mm by 0.1mm: Dormer, four facet ground coated

Metric: 6-10mm by 0.1mm: Dormer, four facet ground coated

A range of Morse taper drills up to 2", mostly odd sizes bought on Ebay for peanuts, used mainly to remove metal fast before boring to size on the lathe.

Boxes full of other drills such as jobbing, stub, spotting, long, extra long, slow spiral and fast spiral acquired or bought as required for a particular job.

I mainly use the metric drill sets, but imperial is useful when working in imperial and the number/letter drills are useful for tapping holes on fine pitch threads, eg, BA and ME, when the metric drill increments are a bit coarse.

I bought my Dromer drill sets from Greenwood Tools. For drills under about 6mm it's a waste of time trying to resharpen them, I just buy a new one, either from Greenwood or my local tool shop. Apart from tapping sizes for M3/M4/M6 I rarely need to buy new drills, the Dormer drills seem to last.

Personally I wouldn't consider cheap drill sets; I need all the help I can get, and quality cutting tools is a good start.

Regards,

Andrew

Hi Lee,

Welcome to the forum. There are no dumb questions, just dumb answers.

I would concur with some previous respondents; get cutting metal as soon as possible. Don't get hung up on 'improvements'. None of my manual machine tools have ball screws or one shot oilers and I haven't found it to be a problem. They've also got lots of backlash, and that's not a problem either. There are two golden rules to machining:

1) Don't buy cheap unbranded cutting tools, however much of a 'bargain' they might appear to be.

2) Know what material you are cutting, who knows what the odd bits out the scrap bin might be.

Seasons Greetings,

Andrew

The oxygen cylinder in one of my two seat gliders was aluminium. Fully charged pressure was about 2000psi. All the cylinders I use (oxygen, acetylene, argon) have bosses on the end with threads in them.

Regards,

Andrew

Mark: Thanks for the link to the NSK website. I've downloaded some of their technical documents. They'll come in useful as and when I re-design the spindle and bearings on my surface grinder.

Regards,

Andrew