I've got a request for a coffee table that can raise or lower from 14" high to 18" high. 

I've got the geometry figured out, but before committing to the final material I like to verify that details will work.

This is my test for a pivot bracket that'll be under the table top and let a leg frame pivot. 

  

Twin tapered tenons into the underside.  Fit is perfect and with a little glue it should never fall out.

Embedded nylock nut needs to be a bit deeper. Should keep the bolt from turning as the leg frame pivots around the bolt shaft. 

Small parts like this are always a good challenge.  How to clamp the board down to cut them out for example.

4D

 

Edited November 28, 2025Nov 28 by 4DThinker

Detail #2.  Barrel nut sliding pivot.

Part of the geometry has to slide and change angle as the table changes height.  T-slot cut in the underside of the table top. T-bolt into a barrel nut.  Nylon  washer to slide between leg frame and table underside. 

4D

Interesting project with creative solutions. Following along for the learning experience.

Pivot blocks for the 3/8-16 shaft which will control the spread of the leg frames as the height changes. 

Lock collars have been order to keep the shaft registered to the right block. 

4D

Revision for the square nut pocket.

I realized that if you picked the table up the nut would come out of the pocket.   To keep it in place I've changed it so it drops in from the top of the block. I'll add a plug over the nut eventually.

 

This will keep the table from changing height configuration when you pick it up. Now I need to decide how to keep the pivot pins in place. 

4D

Pivot block test pocket. 5mm id washer on each side to center the block. Room above and below to tip without rubbing on the leg panel.

Test done in a plywood scrap.  Eventually this will be either cherry or maple.  Haven't decided yet. 

4D

Clever and very clean looking design.

WOW - A huge amount of engineering here.  Look like you got a good handle on it.  Will be looking for the final project.

Picked up two 16" x 48" x .75" red oak panels to make the top and legs from.  Stymied by the postal service who seems to have a hard time delivering needed hardware to my house.  Updates to come.  I don't know when. 

4D 

10 hours ago, 4DThinker said:

 Stymied by the postal service who seems to have a hard time delivering needed hardware to my house.  

 

Don't feel alone with that....it certainly is a problem for me and I suspect quite a few others.

1 hour ago, Fred W. Hargis Jr said:

Don't feel alone with that....it certainly is a problem for me and I suspect quite a few others.

I'll start watching our mail closely. We seem to get ours OK along with several others mail in the neighborhood. I haven't seen any of yours yet though.😜

Edited December 10, 2025Dec 10 by Grandpadave52

2 hours ago, Fred W. Hargis Jr said:

Don't feel alone with that....it certainly is a problem for me and I suspect quite a few others.

Yeah, I am leery of the USPS these days.  Too many reasons to even list.

 

I don't even get home delivery of mail - very common in the rural west to simply have everyone use a PO box.  PO opens at 9 am, closes at 3 pm - if my package isn't in a locker (rare) then I have to wait until Saturday to get it.

On 11/28/2025 at 4:50 PM, 4DThinker said:

Embedded nylock nut needs to be a bit deeper. Should keep the bolt from turning as the leg frame pivots around the bolt shaft. 

Might add a bushing to that bolt and tighten the bolt down against it. It will keep the bolt from wanting to turn and give the leg something solid to turn on.

20 minutes ago, Zack said:

Might add a bushing to that bolt and tighten the bolt down against it. It will keep the bolt from wanting to turn and give the leg something solid to turn on.

In use the leg will only rotate 20 degrees slowly as the design raises or lowers 4". And that would only happen maybe a few times a year as the owner decides to change the height.  Opening the hole for a bushing will weaken the wood around it and increase the chance of it splitting. With the weight of the table and whatever is on it being held down by gravity and the geometry not being changed there shouldn't be any play in the connections/pivot points.  If this was a beefier structure such as a folding chair then your advice is sound and wise.  I also expect to find any flaws of this prototype once assembled and used. It may take another revision or two as many of my designs have before I consider it finished and good. Some things are only knowable once a design is in use.  

4D 

I think this is all the details needed for the leg panels.

1. Insets for the barrel nuts in the middle of the top half.
2. Insets for the pivot pins in the center.
3. Notches on the side with a slot for a square nut.
4. Top and bottom edges rounded over. 

The  bottom of the table top also has all the details cut into it. 

Still needed are the intermediate panels that will connect the table underside to the middle of the leg panels. 

All the needed hardware has arrived finally.  

4D

Found that the t-bolt didn't slide well in the slots, so today I cut some HDPE slides to see if they would work better. 

Took two tries to get a nice slip fit. Second set I added a -.02" allowance to to reduce the width and thickness of the bottom lip. 

I had the CNC cut a .201"d hole and then I threaded them with a 1/4-20 tap.  I'll use short sections of 1/4-20 rod to connect them to the barrel nuts in the leg panel ends. 

4D

Edited December 15, 2025Dec 15 by 4DThinker

Good solution 4D. Wondering if a thin nylon washer (or one made from HDPE) against the head of the standard t-bolt would also work? You still would retain the strength of a one piece bolt with no risk for thread failure.

1 hour ago, Grandpadave52 said:

Good solution 4D. Wondering if a thin nylon washer (or one made from HDPE) against the head of the standard t-bolt would also work? You still would retain the strength of a one piece bolt with no risk for thread failure.

I'm using 1/16" thick nylon washers between the table surface and the leg, as well as between the pivot brackets and the pivot panel, and between the pivot panel and the legs panels. No wood-to-wood abrasion.  I also order a 3/8" thick piece of PTFE (Teflon) to see if it is more slippery than the HDPE sliders.   

During test assembly I discover I didn't leave room for two 1/16" thick washers, one on both sides.  So I made my own 1/32" thick plastic washers.

Punched 1/4" holes in a plastic DVD case, cut out squares with a hole in each, then chucked them into my hobby lathe.

  

Nice perfect washers, each just a tiny bit thicker than 1/32". (.0355").

Write up with all the steps now live on my blog here:  Making Plastic Washers

4D

Thanks for the idea and how-to 4D. I've used milk jugs, water bottles and even wax paper as thickness shims but never thought about making washers. Another round2it project for a warmer day or a month of them.