Thread: Small Fixture Blocks

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Hole Locations marked on a 12.50mm grid from centre

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Holes Centre drilled

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All hole now drilled correct diameter half way though block. I will come the other half from the other side.

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Holes counter bored. I only have one M6 capscrew short enough to fit atm. The fit is a little close, I may have to take it out to 11mm, they currently are 10mmx6.6mm deep.

That me done for today.

-Josh

Here is a rendering of couple of more ideas that I have in regards to these block
Here are pictured 3 50x50x50 blocks bolted together.
3x50x50x50 M6 Tooling Blocks.JPG
Idea 1. Use M6 shouldered cap screws.
They have a larger head diameter at 13-14mm compared to std cap screws (10-11mm) and can more positive locate than standard caps. But also would allow the use of 8mm parallel dowel pins with internal/external thread inserted into block as locating pins or stops.
Idea 2. Make the counter bore for the cap screws threaded for M16x1.0 to allow for inserts to be easily attached to either change the thread or for accessories like DTI's etc.

The down side. I would loose a lot of working surface to gauge off

Let me know what you think.

.

Well I think if four standard cap screws arent going to hold it, four shouldered cap screws wont do alot better.(although, and maybe this is why you are thinking of using them,isn't the underside of a shoulder cap screw head ground? maybe thats just in larger sizes?)

The table I found says M6 shouldered caps screws are 7.987max 7.951min dia. If the blocks are reamed to 8mm wont that make locating the holes and the threads a nightmare?

Wouldnt your other ideas work just as well in M12x1.0 and 7mm?

How many sides aren't going to be counter bored?

A larger c/sink or maybe a small c/sink with a small counter bore might be an idea for the M6 threaded holes.


Stuart

Stuart,
Your right on, using more than one shouldered screws would be a pain. The reason for using shoulder caps at all is to locate two block together precisely. Now that I think about it more I wouldn't need one per block, the sides with 5 counter bores make the centre one for the the shouldered cap all the rest can be normal.

The other point you mention is also spot on I could use M12x1.0 and 7mm holes, I drew it up like that at one stage the "pin wrench holes" were a bit smaller 1.5mm instead of 3mm on the adaptors but that is fine also. I'm just having trouble finding 7mm internal threaded dowel pins off the shelf.

4 out of the six sides are counter bored.

I'm not sure about what you mean about the counter sinks?
-Josh

Hi Josh,
But for the blocks to locate precisely, that hole must be located precisely. Being that you wouldnt want matched pairs I cant see how you are going to do it?(thats not to say you wont come up with a stunningly simple way to do it).

If you are going to use only the one hole, why not ream it 8mm use a dowel and forget the screw?

Are you sure you need 4 sides counter bored(other than your M16 insert. Wouldn't 3 sides (meeting at one corner) be enough? That would give you more flat surface on the sides.

The counter bore takes the load on the female thread away from the face that you want to stay flat. (not really sure it will do much good in this case, but I cant see how it would hurt)

Stuart

Hi Josh, Stuart,

Apologies if this is a dumb idea, but what about using locating pins to handle the block to block alignment, ( would they have to be tapered? dunno.. )

I can't see the cap screws providing much by way of block to block alignment accuracy.

Regards
Ray

PS... Ok Josh explained shouldered cap screws to me.. I get it...

Stuart you are an "ideas man" I'll have a play with the 3 sided version. the only reason I had it on both sides was for when the blocks are mounted together I could bolt from both sides depending on which would be easier.

I'm still thinking about it but at the moment I think to correctly dimension the block so that they have the same centre alignment I would need to make a matched pair of blocks (or v blocks) with an 8mm hole with a centre height >25mm. that way I could suspend the other blocks between them with parallel dowels for a reference centre height and gauge parallel to the table before grinding. It would get me pretty close. I'm really more interested in square than a true straight alignment and the addition of precision holes is just an extension to the idea, if it fails I can always just use normal cap screws. Incidentally I found if I use AFNOR standard shoulder caps instead of ISO standard shoulder caps the head diameter is 11mm which would just clear an M12x1.0 thread. win win win.

3d pdf

Starting to sound like a job for a jig borer

Originally Posted by Brobdingnagian

Stuart you are an "ideas man"

I am............... once in a while one of them even works

Not really understand what how you mean to go about it Josh so I've come up with my own plan.
If you can live with only one 8mm reamed hole.

Take your over sized block, ream 8 mm hole.
grind one face(without a hole) flat.
Fit 8mm pin
sit it on the jig. Clamp to the vertical face.
That give you a fixed distance from the pin to the top face with one square corner.
Rotate 180 with the same face against the vertical face of the jig.
Now you have two parallel faces square to the face against the jig.

Now with one of the two new faces against the jig grind the other two faces.

Then grind then two pin faces however you like.(and this I think is where my plan breaks down but its late*)

You're done.

Wheel wear is your problem. Though I think you can go around again with a second light pass.

This wont work with two.

Biggest problem I see is how close the fit on the pin is.

Bad day to start talking about draws, here is my effort. "no dimensions" lol Assuming 50mm sq blockes the lower sides would be 25ish and the back 50ish high.

At least thats how I'm seeing it now, I might see it differently in the morning.

Maybe grinding a flat on the ends of the pin would help.... maybe it would give you more problems.....

I think in the end it might not be that far from what you meant.

Stuart

*there was a version with two holes but I found a floor in my plan.

I'll do a sketch for the setup in the mean time here is the 300x300x25 plate.
fixtureCollection.jpg

To explain the "one hole" problem.
Once you introduce a second hole it must be
1. on the same plan as the first.
2. 90 degrees to the first
No corrections can be made with grinding to align either error.

Clear as mud?

Stuart

p.s. spinning cubes in your head at 1am does nothing to help either typing or sleep

Stuart,
Here is the drawing of the 1st setup I was thinking of to get the centre reamed hole dimensioned and parallel to the 4 sides. The other axis is a problem I have not got a good solution to yet. As you say they have to be orthogonal to start with and on the mill that might be pushing it to get much better than +- 0.02mm.

I think I could get hole centred it to within about +- 0.005mm if I was really really really careful.

looking good Josh

I think you need to make 2 sets one as a backup in case you damage anything and like any good backup you should store them off site to be safe say in Horsham would be a good spot

cheers
Harty

While we are on the subject of reaming. Who makes good quality solid carbide reamers?
I think I would be looking for 8.00mm, 8.01mm or 8.02mm left hand spiral with a cutter length of ~ 25-30mm with a reduced shank.