Member postings for not done it yet

Personally, I would likely be looking to replace the quick change dovetail fixings for a more conventional hinged alternative. Some of the more expensive cheap DTI's come with replaceable backs. Although I have a couple with dovetail fittings, I still prefer the normal eye and screw type as there are very few times I need to change heads on my mag bases.

I would think cryogenics would play a part somewhere in the production process. Can achieve a DeltaT of somewhere in the region of 500K without too much difficulty, or risk to the heat treatment of the outer race.

As a recent new member I haven't followed this thread before. I was amused about the 'discussion' of superchargers, turbos etc., because large, slow running marine engines of this type have been around for a loong time. Even high revving diesels heve been in use for around 70 years (3000rpm Detroit diesels as fitted in trucks and tractors, per eg). Everyone should know that they need crankcase compression (in the case of motorcycle engines, per eg) or a forced (blower) feed for others, such as the detroits. The detroits have a poppet valve for exhaust, so are probably easier to turbocharge as well as being blown. The difference is that any turbo engine of that type still needs a blower - turbos give no bost until spooled up whereas Rootes type blowers are positive displacement machines. One reason why the blower speed has to be in a fixed ratio to the engine speed in these old engines. Modern electronically controlled fuel pumps can more easily control the injection fuel/ratio, but most of these Detroits in 'pulling tractors' just inject soo much excess fuel that they smoke more than the proverbial train.

Anyway, I will now go back and read this interesting build. Very well done, Dean. I doubt iwould ever make one as complex as that. A veritable masterpiece. Do you intend flying it? How much power are you expecting?

Look under condor lathes @lathes dot co dot uk. Mills are mentioned.

One of my vices is dropping the lathe in back gear for removing the chuck. It is also a vice to leave your vise over-tightened for long periods. Another vice might even be that of using both words to cover up one's spelling.

As above a lower vise, at elbow height, is the best. One can generally adopt a strategy to make it higher, but unless you have something to temporarily stand on it is not so easy, when too high, to lower it. Mine is too high but lowering the bench is not an easy option.

Edited By Richard Balderson on 25/05/2016 19:25:33

I found it interesting, but......

Signage for the venue and parking was a total negative. Should have printed off the stand layout above - there was b/a to indicate where to find any one of the exhibitors on that reeeelly sloow set of overhead screens which excruciatingly slowly showedif the exhibitor, one was looking for, existed.

However, the show itself was good. I enjoyed the aeroplanes and boats, particularly.

Would I go again? Probably not. OK for the avid modeller, but not so for a typical '12'' to the foot' scale hobbyist. No, or few, show prices - virtually all were the same as over t'internet - and I would prefer to have things delivered free if I make a large enou

gh purchase, or pay for delivery if I don't.

I was offered a 20% reduction on one new item (after declining the exhoritant asking price) but even then it was still more expensive than buying locally from a specialist. One major supplier moved me along to the third advisor before being told they no longer offered that particular type of cutter. At least they were honest with their information and did not try to market a lesser quality item.

One screw rotates freely but won't move ir or out so I'm guessing it is snapped. The other three are firmly stuck.

You should not guess. It could be that the refractory, or insert in the refactory has allowed the screw to rotate although it (the screw) is completely intact. It may be that these screws are actually threaded into the metal.

As above, remove by drilling any take remedial action as necessary.

Poster reported for trolling.

Emgee,

I have nothing more to add but I would ask you to check your formula 72/(Pi*d) as it calculates a very fine pitch saw !!!!!!!

l am very glad that you have nothing more to add! Your maths is amazingly poor..

Just look at the units of that formula.

It is number of teeth divided by a length. In Imperial units that means TPI! Using 2.75'' as d, the result is 8 tpi. Using 2.5 (estimate) the pitch is estimated as 9 tpi. There is nothing difficult in that simple equation for you to calculate ''a very fine pitch''!

As you did not even address my query I am considering your replies as totally inappropriate.

The matter is now closed to you. Anyone else may have some pertinent information as to the normal convention for calculating pitch for a circular saw. I most certainly know that for a linear calculation the answer would be the same whether using measurments from tip or root of the teeth and can be different for a non-linear surface.

Bye

I note you still insist the pitch is not the 8(8.3) , you must be using the wrong figures in your calculation.

Not so. I am fully aware of the marked diameter and tooth count. The calculation for about 9 arises from the estimate of the tooth depth. I am quite clear of how you arrived at a figure of 8. I am not mathematically challenged, although I always teach the students to keep their calculations simple and follow that practice myself.. Using an algebraic formula and substituting values is the way to go.

All I asked was whether the outside diameter or the root diameter should be used as the basis of calculating tpi. Nothing more. They clearly will give different results as the root diameter (and thus the circumference at that lesser diameter) will lead to a higher result. I am surprised that you are unable to understand the possibility of two different results depending on how it is calculated.

Yes, I know Pi to more decimal places than is needed for this calculation and I was guessing that the root diameter was around 2.5 inches. I was simply questioning which diameter should be used for a tpi calculation as you appeared to make the suggestion that tpi was relevant and your method was one of two possibles, giving the answer as 8.3 or 9 (in this case). The difference may well be larger with other slitting saws, so I was merely questioning which method of calculation is convention.

BTW, I would always calculate using the calculator values for the whole calculation, never take out intermediate values and introduce possible rounding errors or quoting values to excessive significant figures. 72/(Pi*d) seems much more straightforward!

Yes Michael, for the blade pictured above tooth pitch is calculated as 0,120" which is a shade over 8TPI (8.3).

That depends on how you measure it? If one stretches it out as if it were linear, the tpi would be around 9. Not a lot of difference, just depending on whether one uses the tip diameter or the root diameter. Is there a standard way to calculate it?

I'm not a metallurgist, but would think there are different 'grades' of CI - dependent on microstructure. Some cast iron items just use the cheapest material possible. Like dumbbells. Possibly scrap flywheels from old stationary engines might be different (not saying good, necessarily).

Raglan did, too. Seems like all the best lathes of 60/70 years ago thought of small details like that. Now unheard of because it is extra cost!

AIr flow and pressure is all about the Bernouilli Principle. Higher the air flow, the lower the pressure. Think here of blowing between two pieces of paper, when they actually move closer together rather than further apart. Or aeroplane wings creating lift.

The carburettor has a choke tube, or venturi, where the air is speeded up as it passes through. The lower pressure 'allows' fuel to be drawn into the air stream due to the dfference in pressure c/f the fuel supply (which is maintained at a constant level wrt the jet). Different sized engines need different sized venturi and different sized jets. Some, like the ubiquitous Webber 28-36, had two venturi for differing engine speeds and most need some form of help to maintain adequate operation at engine idle, hence a slow running jet and a power jet(s). Other improvements, to aid atomisation and better mixing of the fuel and air can make carbs quite ccomplicated.

Some carbs have simple fixed jets and some have jets with a 'needle' as control. That can be a fixed (but adjustable) or movable item depending on the type of carb.

Hope that helps a bit.

RAB

Edited By Richard Balderson on 29/04/2016 19:59:16

I am like Phil and think the Raglan is a superb little milling machine I looked for something bigger and settled on really old iron - I have found a Centec 2B which doubles as a vertical and horizontal in a size suitable for a hobbyist and with no compromises. It is far better value than a modern chinese offering, IMO, even though over 50 years old.

As I see it, your conundrum is that of achieving both a central hole and 88mm diameter starting with only 88.9mm.

I'm not an engineer, but would attack the problem in one of two ways.

1) carefuly centralise the workpiece in the 4 jaw chuck using a dti securely held on the toolpost so that it can be retracted, to avoid the jaws. Then centre drill and drill the hole. I would then make mandrel with a wide face and glue (with cyanoacrylate) and screw the workpiece to that, for skimming off that half mm.

2) make the initial central hole rather smaller than final size, mount, as above, and machine the outside diameter to size before sorting out the central hole position and size. An end mill with collet holder would be the choice, to alter the centre of the hole by a small amount as a drill might tend to follow the previous (depending on finished size, even in aluminium)

Hope you achieve both your requirements. It can be tricky with such small amounts to machine off.

RAB