SU: Pivot Point

[wizer]

I'm trying to sketch a TS\router table cabinet and I want a flip up extension table. This is what I have so far.

Down

Up

I can't work out how to set the pivot point so that it goes from the up position which is flush with the rest of the cabinet to the down position which clears the dust extraction and sits flush against the cabinet.

Anyone know some trickery?

 

[xy mosian]

Hi,

I think my brain is going to fall over here, but here goes.
Mark the line on the tab of the hinge parallel to the top of the flap which passes through the pivot point on the tab.
Mark the position of this line, on the cabinet when the flap is both up and down.
The intersection is the pivot point on the cabinet.
Transfer this point to the tab on the flap.

Hey presto! or go away wrong again xy.

Do not do this until you've proven it in some way!

xy

edit
OK! My brain's cooled off a bit.
Ignore the above it will leave a gap in the 'up' position.
I think your hinge tab my need a re-design.

xy

 

[SketchUp Guru]

I think XY is on to it. Copy the flip up table so you have one in the up position and one in the down position. Assuming you want the pivot to be on the centerline of the arm, place a couple guides on the centerlines of the two copies of the arm. Where they intersect, you'll place the pivot.

You could also just place the table in the up position and decide on the location of the pivot. Use that to Rotate/Copy the table to the down position to check for conflicts.

Send me the file if you'd like and I'll illustrate.

Dave

 

[rileytoolworks]

Wizer, I haven't got a f@$%ing clue how to do it, but I like that idea. I may 'borrow' it, if that's O.K?
Apologies for any spelling errors - I've had a few beers and can see three keyboards in front of me!
Now, let's see what I can Drunkbid on on Ebay...

 

[xy mosian]

This should do it.
Picture first description afterwards.

All the information needed to find the pivot point is in a scale drawing.

The drawing is of the cabinet side with the flap in upper and lower positions, but without the pivot arm.
Black lines are cabinet, flap etc.
Red lines are construction lines.
Blue is text.

On the flap points A1 & A2 are the same point in the flap up and flap down positions. They lie on an arc of a circle centred at the pivot point. Joining points A1 & A2 we have a chord of that circle, and drawing a line (C, C) through the centre (B) of that line at right angles, 90°, we have a line that passes through the centre of that circle. The pivot point.

If we imagine a line (E, E) from point A2 drawn through the circle centre, as the flap is moved to the upper position that line moves through 90°. Therefore if we draw the line (E, E) at 45° to the radial line (C, C) which passes through point A2, the intersection with the radial line (C, C) gives the centre of the circle. This should be checked by drawing a similar line (D, D) at 45° to the radial line (C, C) which passes through point A1. The intersection of the three lines should be at the same point (PP), THE PIVOT POINT.


xy

 

[SketchUp Guru]

While Riley was off worshipping the porcelain god , I made up these screenshots to illustrate my solution to Wizer's puzzle.

To begin with, I placed a guide point at the center of the arc on the ends of the support arms. This seems like an appropriate place to put the pivot. Then I rotated the flip up top down 90° as it would hang when down. You can see that the bottom of the extension would have to be inside the base of the cabinet.

So I moved the flip top out enough to clear the back of the cabinet. In wizer's model that's in the red direction.

Then I pivoted the top back to the raised position. There was originally a gap of 20mm but after the move it is 33.810mm.

To return to the 20mm spacing, I opened the flip up top component, moved the top assembly 13.81mm and adjust the length of the support arm component to match.

After that, I checked my work by rotating the top up and down while looking at it from various angles to make sure there are no conflicts.

Note: I didn't leave any sort of gap between the top and the back of the case. You might want to do that though to allow for minor variations in the wood.

Edited to add: XY is faster than I am. Well, he probably got up earlier. Good work, sir.

 

[xy mosian]

Nice one Dave.

Thinks....
Must learn to use sketchup,
Must learn to use sketchup...,
Must learn to use sketchup.......,

xy

 

[SketchUp Guru]

Thanks XY. I think you are.

 

[wizer]

Huge thanks Dave. I awoke with stomach cramps and the D word. Must have been a dodgy Chinese take away last night (that'll teach me). So I've only just had a look at this. Seems to make sense. Obviously the real world timber sizes will differ so I will need to transfer this technique to the actual project when I get to that point.

Riley, feel free to borrow the idea. I must have seen it somewhere but I'm not sure where. A simple butt hinge would have been nice and easy but it wouldn't have cleared the table saw rail.

Where would we all be with our Dave? Still using pens and pencils, that's where