What a silly Vee block this one is!

This topic has 11 replies, 9 voices, and was last updated 2 July 2020 at 16:26 by Ian P.

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2 July 2020 at 11:21 #483472
Ian P
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@ianp
I bought this single V block many years ago at a steam rally. It has been on my bench and frequently used on the drilling machine (mostly) for free hand cross drilling but also for many other tasks. Not being is as new condition its been used as a hammer, as packing in the milling machine and lots of other non precision tasks. Its about 1.5" square and 3" long.

I discovered early on that the relief channel at the bottom of the vee is not deep enough to accept a rectangular object and often though of just using an angle grinder freehand to deepen it, but have never got round to it.

Yesterday I was making a right angle optical device which has a mirror at 45 degrees in a block of aluminium. I sat the part machined item in the V (it had a big chamfer so did not touch the bottom) and found that it did not make full contact with the V faces as if the cube shaped part part I had made was not truly square. After a few moments investigation I found that the V was not a true 90 degrees but more like 92 degrees!

Why would a manufacturer make a vee block at anything other than 90 degrees?

I'm amazed that I have had it so long and never noticed this 'feature' before!

Ian P
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2 July 2020 at 11:21 #27493
Ian P
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@ianp
2 July 2020 at 11:35 #483476
pgk pgk
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@pgkpgk17461
Like yards and metres… metric degrees are a tad bigger..

Or 0.8 of a Radian

pgk

Edited By pgk pgk on 02/07/2020 11:37:30
2 July 2020 at 11:40 #483477
Clive Foster
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@clivefoster55965
Small deviations from the 90° vee angle are probably not as uncommon as one might casually expect. Especially with economy ranges. Surface finish flatness with sides and Vees being mutually parallel are generally more important than exact angle.

The Bal-tec site **LINK** has some nice rabbit holes for folk interested in the methodology of exact alignment and associated things to dive down.

Clive
2 July 2020 at 11:49 #483482
Brian G
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@briang
Was it even manufactured rather than simply made? My first pair of V blocks were made within about 8 weeks of starting training, and only matched each other because they were machined as a pair and even I couldn't mess that up – although I'm pretty sure I could now

Brian G
2 July 2020 at 12:16 #483490
Ian P
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@ianp
I am sure it a manufactured product although I cannot see any identifications marks, it is ground all over and it is really hard steel, I doubt it was an apprentice piece.

Its not easy (for me) to measure the V angle but I estimate its only 1 or 2 degrees greater than 90. Both the Vee's are the same angle too.

Ian p
2 July 2020 at 12:31 #483496
Hopper
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@hopper
Maybe to allow clearance on the side of the wheel when surface grinding each face in a cheap and cheerful mass production setup of multiple blocks at once?
2 July 2020 at 12:40 #483498
Bazyle
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@bazyle
It is meant for holding round stock not rectangular so the depth of the slot and angle are not important. If it were dead on 90 it would only acurately hold ground square stock anyway, regular bms will always be a tad off.
2 July 2020 at 12:56 #483503
Emgee
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@emgee
Ian

You say both blocks are ground to the same angle but do they match if 1 block is turned by 180 deg, ? if they match perfectly which ever way the pair are used it means that both sides of the V are ground to the same angle, rather than 1 side ground 47 and the other side 45 for your estimated 92 degrees.
If the sides are ground at different angles you cannot set-up by clocking between the V surfaces to find the centre.

Emgee
2 July 2020 at 12:56 #483504
old mart
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@oldmart
Now we will all be checking our vee blocks. We have at least a dozen at the museum, donated over the years, about 3 pairs and the rest singles. What matters is that a perfectly cylindrical workpiece is held parallel to the base of the vee.

The 2-4-6 blocks that I bought some time ago and assumed to be good turned out to be parallelograms and are awaiting a skim on a big surface grinder. It doesn't matter what size they are but they should match and have square sides.
2 July 2020 at 15:39 #483526
Clive Hartland
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@clivehartland94829
That type of 'V' block is normally sold and used in pairs, I have never found pairs that are the same size.They come with a clamp that fits the side grooves. As I only ever used them for round shaft work or setting the graticules in telescpes I never had a problem.
2 July 2020 at 16:26 #483532
Ian P
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@ianp
Posted by Emgee on 02/07/2020 12:56:24:

Ian

You say both blocks are ground to the same angle but do they match if 1 block is turned by 180 deg, ? if they match perfectly which ever way the pair are used it means that both sides of the V are ground to the same angle, rather than 1 side ground 47 and the other side 45 for your estimated 92 degrees.
If the sides are ground at different angles you cannot set-up by clocking between the V surfaces to find the centre.

Emgee

I only have the one block, what I meant was that both sides of this block have ths same included angle.

My guess at 2 degrees was way off. I have just measured the angle using a (presumably pretty accurately square) gauge block and feeler gauges and its nearer to half a degree. So what I would expect to be 90 degrees is nearer 90.5 degrees.

I do have some pairs of Vee blocks and each pair have matching numbers on them, presumably matched pairs.

Whilst this wonky one has no identification marks, the quality of the grinding examined closely with a strong magnifying glass looks better than an Eclipse pair which claim to be to toolmaking standards (whatever that may be).

I know these blocks are primarily for holding round stock but its not their only purpose.

Ian P
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