Spring holder

[mikejohn]

I have experianced a small problem a couple of times recently.
Working with solid timber materials, I need to clamp down by using a strip of wood crossing the wood I'm cutting (a caul?).
Taking care that the collet remains above this, I've happily cut away, only to hit the 'caul' with the spring holder.
If I 'shorten' the spring by mounting the holder so it is above the bottom of the Z carriage, is this going to cause any problems?
..............Mike

[paco]

Hi Mike!

Take a moment to see how thing are moving and how they are fitted... I've installed the router mounting lower than suggest (default installation) so I got more room all around the lower part of the router motor. This as "free" the dust foot too so it's now easier to change tool bit and I've install the Z tour one hole up too so I now have more clearance... just benefit so far!

[gerald_d]

"Shortening" the spring by 25mm over 500mm is very unlikely to cause you a problem. You weren't concerned about the mass of your bracket, or the mass of your router, so why worry about making the springs 5% "weaker" now? Anyway, if you do see an issue, raise the top end of the spring too...

(Look at the top (later) pics in this (http://www.talkshopbot.com/forum/messages/2/4095.html) thread. Those "staples" are half links of chain welded to the back of the z-slide. The bottom (earlier) pics gave us the same problem as you have now.)

[gerald_d]

In case you are wondering, our springs are not inside the square tubes - they are between the tubes.

[mikejohn]

I did wonder!
Now a question not dissimilar to the above.
I notice today that I can plunge the collet down to table top height. (I didnt have a bit in!!)
My very shortest bit sticks out 9mm.
I have only once used wood at 100mm thick, and I cut OK.
Now I ask myself, what is the purpose of this travel down to the table?
My collet is about 25mm below the base of the router bracket, which is at the same height as the bottom of the z carriage.(although the spring is lower!)
I guess I could raise the router so that the bottom of the collet is in line with the bottom of the Z carriage, but does this give me any great benefit?
I realise I can go over the edge of the table and cut below the table, but can't think why I would do this.
Anyone any thoughts on this?
.................Mike

[paco]

3265

Do you like this?

It can retract to clear the collet from under the AL tube of the gantry and it can touch the collet with a 1" thick spoilboard... and it has more room around the router motor... easier to remove the dust foot...

Notice which holes were used to mount the Z to the carriage, which holes were used to mount the router mounting to the Z rails...

[gerald_d]

"My very shortest bit sticks out 9mm" - at your age, that is normal.

Are the 2" square tubes of your z-assembly drilled with more mounting holes so that you can move the whole assembly higher up in the y-car? Then the "extra" travel makes sense, but realise that the z-slide then protrudes further from the support V-roller, making it less stiff.

Your machine is billed as having a 6" vertical cutting "area" - what happens if you lay a 6" thick job down on your table? Will your gantry go over it? Will you get a collet (and cutter) over the job? I think that the z-assemblies are mounted low for best stiffness, but can be mounted higher to meet the billed 6" spec. (The specs give both 0.15m and 0.18m as being equivalent to 6")

[gerald_d]

On the issue of the length of slide sticking out past the bottom V-roller.....

We have a double set of V-rollers at the bottom. When the Z-slide is fully up, it actually pulls out of the last pair of rollers.

The flex in an overhanging (cantilever) beam is according to the cube of the length (L3). Try this simple test; clamp a plank to your workbench so that it sticks out by 1 foot, measure how much it deflects if you put a brick on the tip, then let it stick out by 2 foot and see that the same brick gives 8 times the deflection. (The same applies for length of cutter sticking out from a collet) ref (http://physics.uwstout.edu/StatStr/statics/Beams/bdsnp412b.htm)

[mikejohn]

Thanks Paco and Gerald
I will ponder options and report back.
"at my age" just goes up one today, so be nice to me for 24 hours!
......................Mike

[gerald_d]

Happy Birthday Mike!