Quasi-involute V-block

[mklotz]

Bear with me on this one; it's going to take a bit of background to get to the point.

When I was first starting out I decided that, if I intended to use tools, I should know how they look and what they do. My approach, which I heartily recommend to all neophytes, was to go through the MSC catalogue page by page. If I saw a tool whose purpose or use was unknown to me, I would investigate until I understood it even if it was something I'd never own or use. What I learned by this exercise has been of immense aid to me ever since. Understand, this was all done in the days before the internet so it was time consuming and often tedious. However, if you don't have the patience to apply yourself you'll have real trouble developing skills; plus, today, with the internet, it's ever so much easier to discover what things are and how they work.

Too many people, encountering a new object or mechanism whose purpose they don't understand will blow it off with "Who knows?" and rejoice in the fact that they've yet again avoided learning something. Need I say that that is a bad attitude in wood and metal working and an even worse attitude in life?

OK, back to the subject... One of the new-to-me things I encountered while doing this was a Starrett precision level with an involute base. I puzzled over that base for quite a while before I understood why that was desirable. I tucked that bit of learning away and went on. The level was so bloody expensive that I'd probably never own one (I do own a less expensive version now) and, even if I did, wouldn't need the involute feature.

So, one day rooting around in my favorite supplier of aircraft aluminum offcuts, I stumble upon a piece that has a profile like this...

I flashback to my early catalogue-reading days and say, "Why there's an involute V-block lurking in that." Scarfed it up and, as the picture shows cut it into several pieces to use in the milling vise.

Now, to be fair, it's not a true mathematical involute as used in designing gear teeth, but it's very similar and I need a single word description to keep this already lengthy post shorter, so I'll continue to refer to it that way.

Why do we need or want involute V-blocks? An ordinary, straight-sided V-block isn't much good for locating parts with a diameter greater than the width of the mouth of the 'V', as this picture demonstrates...

Any side pressure on the bronze bushing will easily dislodge it from the V-groove.

But an involute can provide reasonable support for a much larger range of diameters.

The central slot is 0.5" wide so this involute V-block can handle material from slightly larger than 0.5" up to the 1.5"+ diameter of the bronze bushing in a block that is only 0.5" thick.

Let's look at a practical application. In a previous thread...

http://www.homemadetools.net/forum/p...5615#post82203

I described a prismatic 'V' jaw I made for the Panavise. As is obvious from this picture...

using it to secure a large diameter part is a non-starter. So I made an involute jaw and it accommodates the part handily...

The involute jaw has two strips of wood glued onto the back to locate it on the existing Panavise jaw. Also glued there are two supermagnets obtained from Harbor Freight...

Rare Earth Magnets - Rare Earth Magnet Set, 10 Piece

which keep the jaw in place.

I was lucky to find my involute form stock but you can easily make your own. Woodworking tools work well in aluminum. After milling out the central slot between the two involute walls, use a router round-over bit to form the quarter circle walls. I'm not a woodworker but I'm guessing that, for a woodworker version, one could glue strips of quarter round to a baseboard of some sort.

Even if you don't build one, keep the concept in mind; you may need it some day.

[Paul Jones]

Marv,

Wonderful story and background. The involution profile jaws are a great addition to the shop. Your aluminum drops gives us hope there may be an aluminum extrusion that may be available for general sale. Your advice about going page by page through the tool catalog is so true whether being a novice or an expert because there is so much to learn (or be reminded of what was forgotten) and image.

Thank you for the posting and excellent photos,

Paul

[tonyfoale]

An ordinary, straight-sided V-block isn't much good for locating parts with a diameter greater than the width of the mouth of the 'V', as this picture demonstrates...

Marv,

Small correction. The mouth of a vee-block need only be greater than 71% of a round piece diameter to hold it securely. Any extra width adds nothing.

[mklotz]

Marv,

Wonderful story and background. The involution profile jaws are a great addition to the shop. Your aluminum drops gives us hope there may be an aluminum extrusion that may be available for general sale. Your advice about going page by page through the tool catalog is so true whether being a novice or an expert because there is so much to learn (or be reminded of what was forgotten) and image.

Thank you for the posting and excellent photos,

Paul

I really don't think that making one's own imitation of my extrusion would be that difficult. There are all sorts of "rounding over" router bits available. The equivalent metalworking tool is puzzlingly labeled a "corner rounding" bit despite the fact that its job is to round edges, not corners.

Making a true involute would be much more difficult - a task for CNC. There are actually three types of involutes - circular, parabolic and elliptical. I think, but am not certain, that the form used on the bottom of levels is a parabolic involute. Regardless, the mathematics of any of the three are a bit complex...

Wolfram|Alpha: Computational Knowledge Engine

[mklotz]

Marv,

Small correction. The mouth of a vee-block need only be greater than 71% of a round piece diameter to hold it securely. Any extra width adds nothing.

I believe you, Tony, but could you show how that number is derived?

[tonyfoale]

I believe you, Tony, but could you show how that number is derived?

Firstly, that is only true in the case of the vee-block having a symmetrical 90deg. Vee, but that is generally the case.
I suggest that you sketch it out and it will become obvious.
A round bar will contact at the tangent points and hence the angle between the radii to the two contact points will also be at 90 deg. So the horizontal distance (vertical in your vice application) between the contact points will simply be the hypotenuse of a rt. triangle with the other sides equal to the bar radius, R. which Mr. Pythagorous indicates is R x sq.rt(1x1 + 1x1) = 1.414141414 x R. The bar diam = 2 x R.
Therefore the contact points are 1.4141414/2 = 0.70707 x D apart. I said you needed 71% to give a little latitude over the actual 70.707%.

[mklotz]

After writing that I went into the kitchen to make tea. While filling the kettle it came to me - radius must be perpendicular to the V-wall which means the half width is 0.707 times the radius and the full width is twice that or 0.707 times the diameter.

Note to self - think more before typing.

[Toolmaker51]

This discussion on involutes is more than interesting; including proper sizing per diameter of conventional Vee blocks. The Vee in spirit level tool height setting gauges is purely inadequate. Why those 'um...gineers' don't get it is beyond me.


Add another vote on printed material in founding knowledge of tools. My 'texts' were the American, Ducommon, and McMaster-Carr Hardware catalogs. The American and Ducommon were wholesalers and distributors, are 1930's era and hundreds of pages. As a worldwide supplier and ship-to service Mcmaster-Carrs' secondary value is estimating weight and identifying unknown tools and hardware. Often easier than the 'net too.

[tonyfoale]

After writing that I went into the kitchen to make tea. While filling the kettle it came to me - radius must be perpendicular to the V-wall which means the half width is 0.707 times the radius and the full width is twice that or 0.707 times the diameter.

Whenever I see numbers or something geometric, any "errors" just seem to shout out at me. OCD perhaps?

Note to self - think more before typing.

Sound advice for us all, we all suffer from insufficient thought at times.

[DIYer]

Thanks mklotz! We've added your Quasi Involute V Block to our Workholding category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Quasi Involute V Block by mklotz

tags: V-block