when is a precision vice not a precision vice>?

[alan smith 6Participant @alansmith6]

Francis, I`m not really into Chinese culture, It just amazes me how Europe has given away it`s technology free to China just to make a profit and lost it`s industry in the process. I have tried to warn folk of the consequences for years but nobody listens. It`s just like the forum!

I look forward to JS taking delivery of his Chinese look-alike Roller it will look good to his clientel, who wants an Audi anymore anyway, At least with the Chinese Roller you get a mechanic thrown in for the price. Perhaps JS can train him up on the ever shrinking and expanding TOS.

[Anonymous]

Posted by MICHAEL WILLIAMS on 28/01/2013 13:57:52:

Rigidity , accuracy , repeatability , squareness and minimal jaw lift are basics but there are many more considerations .

Such as, I can think of parallelism, but what else? – Andrew

[Anonymous]

Posted by alan smith 6 on 28/01/2013 21:03:55:

What`s wrong with tapping the work down with a lead hammer as has been done since the days of Josia Whitworth. OOPs, forgot that those flimsy Chinese mills would probably break in half if treated in that way.

Because it's a waste of time, quicker to use a vice that has minimal jaw lift instead.

Andrew

[alan smith 6Participant @alansmith6]

Andrew,

Sleeping is a waste of time!

Alan

[Anonymous]

Over the years I've acquired a few vices, but we won't go into that on a public forum.

In terms of machine vices I've got an 8" Abwood on the shaper; looking at the vice I think it was originally intended for a shaper. It cost £25 on Ebay, and it's staying on the shaper because it is too heavy for me to lift. For some years I used a 6" vice for milling that came secondhand with my vertical mill, thrown in as a deal sweetener, now I know why. I thought it was an Abwood, but having just looked I can't see any makers name. It has a few drill holes in it, not by me I hasten to add. In the end I go so fed up with the jaw lift on it I put it to one side and bought a Kurt D688. Expensive but well worth it, although of course I would say that!

I've also got one of those 'bolt to the mill table vices' for long parts; bought secondhand on Ebay. Actually I bought two, and sold the second one for comfortably more than half of what I paid.

I also bought a small Soba universal swivelling vice for use on the Clarkson T&C grinder. It'd be nice to have an original Clarkson or J&S vice for the T&C grinder, but they're pretty rare, and go for silly money. After all it's only for grinding lathe tools, not precision surface grinding.

I've also got a lovely toolmakers vice, made by the late father of a friend of mine, who happened to be a toolmaker.

Regards,

Andrew

[alan smith 6Participant @alansmith6]

Andrew,

With a comeback like that, all`s forgiven.

Alan

Ps. is that a tractor you`re driving?

Edited By alan smith 6 on 28/01/2013 23:35:05

[Anonymous]

Posted by alan smith 6 on 28/01/2013 23:33:06:

Ps. is that a tractor you`re driving?

Alan,

Close, it's actually a Pawnee 235, and I was about to tow a glider into the air. The Pawnee is an ex-crop sprayer, and is known as an aerial tractor; simple and basic, but gets the job done. Here's the whole thing:

The picture was taken a while ago, the 'sharks teeth' no longer adorn the cowling. Neither does the engine at the moment, but that's another story.

Regards,

Andrew

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Rigidity , accuracy , repeatability , squareness and minimal jaw lift are basics but there are many more considerations .

Such as, I can think of parallelism, but what else? – Andrew

An important further consideration when actually designing a good machining vice is what happens to moving jaw and work as the screw is tightened to hold . Good design here can make all the difference between a vice which works perfectly and a vice which is barely adequate and irritating in use .

The force on the jaw as provided by the screw ( either directly or indirectly ) is quite big and can cause a jaw which is not properly guided to flip up , down or sideways to the limit of clearances . So good design controls clearances in all directions (including laterally) as far as possible and applies screw force in location and by means which tend to stabilise jaw – ideally push it downwards to compensate for jaw lift .

Positioning of the centre of thrust correctly on the jaw is usually a good start – roughly the higher up on the jaw the better . Some sophisticated vices for special purposes have an arrangement of opposed wedges which transmit screw force in such a way as to generate a down force on the jaw .

The pitch of the screw also has an important effect on the correct working of a machining vice . Ideally when user feels that vice is ' tight ' as felt through the handle it is in reallity ' tight ' at the holding position between the jaws and work is correctly held . Too fine a pitch and excess work holding load are generated and too coarse and inadequate work holding forces are generated . Excessively coarse threads can have the additional problem that they don't lock and vice will creep loose especially in presence of vibration .

There are many more considerations which apply to all machining vices but which have more relevance to higher precision ones . Some of these are related to ' ease of use ' and include mounting and alignment .

Regards ,

Michael Williams .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Remember the American pilot that was ferrying a crop duster across the Pacific to Australia (or NZ ? ) and who became disorientated and lost ?

A civilian airliner was the only thing flying in the right region and Captain on board decided to find and rescue the American The true tale of this feat of intuitive seat of the pants navigation and successful finding of the lost pilot is fascinating .

There was a feature film made of the story – no doubt embroidered a bit – but essentially realistic .

Michael Williams .

[Anonymous]

Michael,

Thanks for the elucidation, there's always more to things than meet the eye. It would be interesting to know how many manufacturers take all these factors into account.

My Kurt vice manual lists clamping forces of well over 7000lbs, depending upon the torque applied to the screw.

Regards,

Andrew

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Probably most of the best vice manufacturers incorporate the same sort of thinking in their designs . Not nescessarily in a rigorous way but more as the intuitive application of experience of what works and what doesn't over many years .

Full analysis of what happens in the screw – nut – slides interaction is certainly done commonly in CNC machine design .

Theory and experience are often described as wholly different things – almost mutually exclusive . Nothing could be further from the truth – the two merge together seamlessly over time to become a unified body of knowledge .

The depth of analysis that goes into design of components and assemblies in some industries is very great indeed whereas in some other industries it is minimal . Its just a question of doing what is appropriate for the task in hand .

Michael Williams .

Edited By MICHAEL WILLIAMS on 30/01/2013 12:14:49

[Gray62Participant @gray62]

Ahh happy memories Andrew, we had a pawnee at Bicester when I was in teh RAF, was the best tug on the field, although the Supermunk came a close second

The only problem we had with the Pawnee was that it tried to rip the wings of a K8 or K18. Great for towing out a Blanik though, would love to give one of those old tin tubs another rove around the skies

CB

[Ian S CParticipant @iansc]

Interesting Andrew, the prop appears to be fixed pitch, is it metal, wood, or some other construction?

Ian S C

[Anonymous]

Ian,

Yes, it is a fixed pitch prop; fairly fine pitch for towing, so good acceleration and climb performance but a bit slow in the cruise. As far as I'm aware it's a wooden prop with a fibreglass/paint protective layer. Primary reason for a four blade prop is that it is quieter than the normal two blade metal props originally found on Pawnees.

Regards,

Andrew

[Chris TriceParticipant @christrice43267]

Presumably a slightly smaller diameter too which gives it a bit more ground clearance?

[Ian S CParticipant @iansc]

Chris, if the prop dia is reduced, its not for extra clearance, the old two blade prop had enough clearance to opperate from rough farm airstrips in NZ. The reduction of dia reduces the tip speed of the prop, normally the tip speed is very near the speed of sound, and that is where the noise comes from. Even the early Spitfires and Hurricans had fixed pitch props, they had the opposite problem, very poor low speed, course pitch, high speed, from a two blade Watts wooden prop. Ian S C

[Anonymous]

Chris,

You are correct, the prop is smaller in diameter, so the ground clearance is better. However, as Ian says, this is not normally a problem with Pawnees. For some taildraggers it can be, like this:

This prop is variable pitch, so another lever to play with. I need to carry checklist cards when I fly this aircraft, in case I forget something. Ground clearance is often worse with tricycle undercarriage aircraft.

To a first approximation the power absorbed by a propellor is proportional to the area of the propellor disc versus the percentage of that area occupied by blades. So, if the power is constant, adding more blades means that the diameter can be smaller. Again, as Ian says, that means the tip speed is lower, and hence less noisy. Noise is a particular problem with tugging as we use full power from takeoff to the top of the tow.

Regards,

Andrew

[Chris TriceParticipant @christrice43267]

Ian, generally if you increase the number of blades, you decrease the diameter as the propellor is matched to the engine horsepower x the duty it's intended to perform. A fixed pitch propellor is like being in a car with only one gear. The number of blades on the aforementioned Spitfires and Hurricanes went up with the engine horsepower because they couldn't make the the propellor bigger in diameter without hitting the ground. Again, generally speaking, two blades are the most efficient because they're less likely to be in the prop wash of the preceeding blade although at high speed this becomes less of an issue.

[Ian S CParticipant @iansc]

Yes Chris, thats it, there were all sorts of methods tried to get the power harnesed, 5 blades, contra props, the reason for the cranked wing on the Corsair was the extra large dia prop, even when they went to 4 blades.

Andrew, you'v got to remember the shutters on the front of the engine cowling, I suppose the Russians need them in the winter. Ian S C

[Anonymous]

Posted by Ian S C on 03/02/2013 10:21:27:

Andrew, you'v got to remember the shutters on the front of the engine cowling, I suppose the Russians need them in the winter.

The shutters are useful on the descent off tow to prevent engine cooling, but the golden rule is to make sure that they're open before take off, otherwise it gets stinky pretty quickly (burnt oil), followed by an overheated engine.

Andrew

[PeteParticipant @pete41194]

When is a precision vise not a precision vise? When it's exactly what you found. But advertising specializes in half truths if not direct lies. This is a fairly long thread, and I did read all but the OT posts. There seems to be a bit too much posted here where people don't seem to quite understand logic and basic thinking about economics though. There is and never will be any such thing as good, accurate, and cheap.

To name just two people, I've been reading both John Stevenson's and Jasons posts for a long time. Both without fail always freely offer as much of their experience as possible. And both have a very large amount of that experience that anyone here with a lesser amount would do very well to pay close attention to what they have to say. You might even learn something if you ever get past your own personal biases.

I certainly don't expect anyone here to embrace my way of doing things since everyone is of course different.

But even with this being a hobby for most. Exactly why does that mean were under no need to do our own product research? I guess if you don't own a computer, then you'd have some reasons for not being able to do it as well as those who do. I doubt anyone here are managing to get their own thoughts posted here by or with a crystal ball. So…………………………………..

I've slowly learned by a lot time, trial and error, and wasted money that there are areas where you DO NOT buy on price alone. Work holding would be just one of those. Shortly after buying my Taiwan built Bridgeport clone, I bought two 4" capacity Kurt style Chinese built mill vises. Due to my job at the time, it was over a year before I was even able to get them bolted down to the mill table. And I used one of those vises exactly once. The fixed jaw deflection, trueness of that fixed jaw, internal machining, or to be more honest, the lack of internal machining never mind accurate grinding, etc,etc. All of it added up to a pair of vises that were useless. Yes I can or I could remachine them to be much better than they are now. But I can't fix the basic bondo filled weak castings, or the quality of the cast iron that was used either. They look ok, it's when you start to actualy dig into them when you find out there not even a basic casting kit that can be reworked to be suitable. I then bought what I knew very well I should have but didn't to begin with. A matched pair of Glacern 615's. At $1,000 plus shipping for the pair of them, it really did hurt my wallet. But I won't ever need better no matter what work shows up given the accuracy an average Bridgeport type mill is capable of producing. These vices are fully able to match and exceed anything myself or this mill is capable of. But I bought them after a lot of research about what would get me the most performance for my money. That was also buying a nessisary product and using proper logic while doing so. Even at the hobby level, everything we do should be based on the bare minimum of using some logic.

Yes I fully understand the problems that the entry level people are going through in regards to choosing tooling or even paying for it since there is so much that seems to be needed right away even to do the most basic of jobs. I can't help you with that problem. I can list some of my experience, and it's then up to them to pay attention to it or not.

I've always made a point of buying the very best metrology equipment I can afford since if I can't depend on reliable readings and measurements, then I may as well just use a carpenters tape measure. So far that idea has worked well.

But I've personally decided for myself after buying those worthless mill vises that I can no longer afford to buy cheap, or to word it a bit better? Poorly built tooling or cutting tools. And I've yet to buy anything at a cheap price for this hobby that was worthwhile. That was a hard and expensive lesson to finally learn, but it was a true one. Yes it does hurt a bit to make a point of buying proper industrial quality. But it hurts far more to buy junk to begin with and then replace it with what's really required. And those much higher cost cutting tools work out cheaper due to there dureability, faster metal removal rates, and much better finishes. Our usual lower horse power equipment can also stand all the help they can get by using tools that do come as proper and real high quality HSS or Carbide, and then they even come properly sharpened. And before you protest that you can't afford that industrial quality because this is after all just a hobby? If you haven't actually tested some of it, then just how do you know and exactly how do you think any of your points of view about them are even valid or logical? In fact, if you haven't tried any of it, then you don't have enough experience to say if I'm even right or wrong. Tooling is exactly the same. "It's only a hobby, better isn't needed" Uh huh, and when something shows up that does need better?

All high quality tooling should list some specifications for accuracy, runouts, etc. A mill vise for example should list just how true the bed and fixed jaw is. But when tooling doesn't have any specifications listed. I just don't buy it. What are your complaints then? You have nothing measureable to check or judge it against.

Pete

[John Stevenson 1Participant @johnstevenson1]

Pete, well said.

The cheques in the post………….

[Brian WoodParticipant @brianwood45127]

Like Pete I have followed this thread and in some places with concern or at least amazement. The common sense expressed by Pete was a refreshing change, long may it be so.

I have made the same painful discoveries for myself and as a result have haunted bankrupt stock and industrial tool sales to be able to buy better quality at prices I can afford, usually with success.

It is good to back your judgement at these events too, you quickly learn who is knowledgable and who is just a scrappy on the hunt..

Brian.

[Anonymous]

Hmmmm, some valid points made by Pete, just a pity he felt the need to be condescending.

Andrew

PS: Must remember to doff my cap and bow next time I meet JasonB

[Brian WarwickParticipant @brianwarwick88192]

Posted by Andrew Johnston on 11/02/2013 12:22:55:

Hmmmm, some valid points made by Pete, just a pity he felt the need to be condescending.

Andrew

I couldn’t agree more, I think this thread is just going around in circles, I doubt anyone could argue quality costs but not everyone needs Rolls Royce quality so if a person is happy with a lower spec because it fits their needs then that’s fine. But those that buy a piece of equipment for scrap value and with no specification don’t whinge when a heap of scrap arrives either return it or accept that’s what you bought. Bottom line is QUALITY is FIT FOR PURPOSE nothing more nothing less after all a spec could say +/- 1" and a prodcut would be classed as quality if it was within tolleance based on the spec.

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