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DCM shock mount installation;

Section
Repair
- 03 Nov 2017 -
8 posts / 0 new
#1

I've come up against an odd problem related to the installation of new shock mounts on a DCM. The mount at the middle of the seat does not sit flat against the seat. I am not sure what to conclude from this. Has the frame been bent? There is no sign of bending damage. Am I missing a shim of some short that would adjust the angle of the shock mount? I am certainly not going to continue with the installation of the mounts until I find a fix for this situation. Advice would be much appreciated.


DCM shock mount installation;
Designer(s)
Producers
Country
United States
Functions
chairs & stools
Periods
1950 - 1959

Comments

- 03 Nov 2017

Appears correct. When the shock mount is adhered securely to the bottom of the seat panel, the resiliency of the rubber compound will allow it to eventually conform somewhat to the frame member. When new, it does only contact frame toward the forward portion. I've found that periodic re-tightening of the screw is often needed for the first few years as this design quirk sorts itself out.

- 03 Nov 2017

Thanks for the quick reply. I have found some on-line photos of old DCM shocks that confirm your advice that the shock eventually conforms to the frame. Still, that gap bothers me enough that I will probably make a tapered disk shim to bring the shock up flat against the seat. The twisting/prying forces applied to the shock if it is installed without a shim will be significant. It seems that they would severely tax the integrity of the new shock and the glue bond to the seat.

- 03 Nov 2017

It may be better to have the surface contact the frame more evenly, but they seem to work and hold up just fine anyway. The worse part of this, IMO, is that the axis of the hole in the frame and that of the threaded insert in the shock mount are misaligned when installed as designed as is the case with my set of 4 purchased new in 2000. It seems a bit odd to me that HM hadn't dealt with this issue at some point before then. It wouldn't take much.

- 03 Nov 2017

Not sure I exactly understand you explanation of the hole alignment problem. In a previous post I showed how the rear legs on my project chair were apparently welded on backwards. I wonder if It's possible that in the early years of production there was some amount of handwork being done. Holes might vary from one chair to another.

Here are a couple of photos of the shim I made for the center seat shock. Material is merbau, an extremely hard and tough tropical hardwood. Diameter is 1.4 inches with a 5 deg. taper. I'm more comfortable now with the shock alignment.

- 03 Nov 2017

Shim looks fine. If it fails, no harm, no foul assuming it's not glued to the mount. On the later editions (mine), it's a smaller-diameter screw on the center seat mount than all of the others.

Whose replacement mounts did you buy? What are you using for glue?

- 04 Nov 2017

I'm using the Special K Products mounts and glue. Had debated whether to order their glue but decided yes.
Just mixed up a small test batch. Interesting stuff. It cures fairly quickly and remains more flexible than standard boat-building epoxies. No tendency to crack or shatter. Cures to about the consistency and bend characteristics of polyethylene. I am optimistic that it will perform well over time on the shock mounts.

- 04 Nov 2017

I haven't seen theirs. I've used OEM mounts on DCMs and an ES670 with PC-7 as per Alfie Hume's advice and have experienced no failures or signs thereof to date (knock wood veneer)...

There have been advances made since venerable PC-7, though, as far as 2-part adhesives. Two that I've been curious about for similar applications are West System "G-Flex" and "Plexus" by ITW. 3M, of course, now offers a dizzying assortment of specialized, high-performance products, too, but they make it difficult for small-time operators like me.

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