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Module Standards for HO scale, re: T-nuts

I was looking for NMRA Standards for HO scale modules and found several sites with the information. One thing bothers me though, and that is the method of adjusting the height of the tables. The drawings called out 1/4" or 5/16" hex-cap screws (bolts) and T-nuts.

The T-nuts are inserted in the bottom end of the leg and the cap screw is threaded into that.

Very poor design. In fact, it doesn't even deserve to be called a "design".

There is nothing to keep the T-nut stuck into the leg except the weight of the table on it. I will bet that most people have been plagued with the T-nuts falling out all the time while transporting and setting up / knocking down the modules. T-nuts are meant to have a threaded fastener driven into them from the end OPPOSITE the end or side where they are inserted. They are not meant to be self-securing. Using T-nuts as shown in the spec sheets is abominable engineering. In fact, it is not even engineering at all. It is hack-work.

There is a device engineered for the task of constructing adjustable height legs that is called a threaded insert. Actually it has more than one use, but it is the most perfect thing for the purpose here. The companion to the threaded insert is the fixed or swivel foot. The threaded insert is a piece of metal with wood screw threads on the outside and nachine screw threads on the inside. For example: drill a hole 11/16 in the center of the leg and screw the threaded insert into it. On the ones I buy, this is done with an Allen wrench. Support the table by inserting a foot with a 3/8 machine screw thread into the insert. The foot, which has approximately 2 square inches of weight distribution area as oposed to the

1/4 inch area of a cap screw, has an adjusting hex at the bottom and a jamb-nut to secure against the bottom of the threaded insert once you have the adjustment fixed. A most elegant and effective solution that is rock-solid and stable. Once you have the jamb-nut tight nothing will change until YOU change it.

Threaded inserets are not usually sold at places like Home Depot, but sometimes you can find them there. A better bet is a good hardware store such as ACE or Tru-Value. Independent hardware, home supply and farm supply stores will often have several sizes in stock along with the companion feet. Look for inserts that have a

1/4-20, 5/16-18 or a 3/8-16 internal thread and get the correct companion feet.

Here is an index of SAE threads:

COARSE:

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FINE:
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Trash the T-nut! Do it right.

Reply to
Froggy
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Whilst I see your point about there being better engineered solutions, out group has used this method for at least 10 years now on all our porable layouts and we have never had a nut fall out yet. Driling the mounting hole so its a tight fit and then hammering the nut in seems to hold it very tightly.

Regards,

Stuart

Reply to
Stuart D.

Eeeekk.Gasp!

I can't believe you actually put that in print! Aaaaaakkkk! Oh, 'Lizibeth, I'm coming home honey (clutches left side of chest and staggers to couch))

.............F>

Aghast, GA.

Reply to
Froggy

Agreed. That said, I've never heard of one falling out under any condition other than a loose fit or being pulled by the bolt. And a little epoxy goes a long way :-).

But as a woodworker I heartily endorse the use of threaded inserts (or barrel bolts) instead.

Reply to
Larry Blanchard

Oh dear.

Then you won't want to know my leg height adjuster is a 3" x 3/8" coach screw screwed into a drilled hole in the bottom of the leg and adjusted with my trusty shifter? No? Thought not. :)

Steve Empirical Engineering, NSW

Reply to
Steve Magee

Check the module standards at

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and click on module specs. We do not use T nuts for the very reasons you stated. We use threaded inserts which can be found at woodworking supply houses and at McMaster-Carr. For adjustment we use 3/8-16 4" full thread carriage bolts. These have worked very well for well over 10 years.

Larry Madson

Reply to
larry madson

Heck Froggy..... to adjust height just use a block of wood and a bottle jack. Works fantastic with 2x4 and 2x12 L-girder benchwork with 4x4 legs and concrete over rebar hard-shell scenery. And the same piece of hardware works on the pickup too. :) Bruce

Reply to
Bruce Favinger

We've used T-nuts for almost 20 years now, and while some module legs have lost T-nuts, a snug fit and a little epoxy pretty much solves that problem. T-nuts are relatively cheap and commonly available, which is a big plus.

While most modules still have their feet, we now level with

3x3 inch shims in 1/8" increments. One end of a module is supported by it's neighbor, then the other end is brought to close to level with the shims, then we move onto the next module. It's much faster (and easier on the back) than adjusting the bolts, and hasn't created any operating problems.

Chris Johnson

Reply to
Chris Johnson

I haven't even been that fancy. For ten years I've used 2x2 legs, with just a plain old 5/16 Lag screw threaded into the bottom of the wood.

Easy to adjst with a wrench, and haven't lost one yet.

Don

-- snipped-for-privacy@prodigy.net

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Reply to
Trainman

Ohhh, the pain........

..............F>

Dr Smith, GA

Reply to
Froggy

Yeahbbut, DON, where is your sense of elegance of design?

This is gettin worse an' worse :-(

Reply to
Froggy

Reply to
res0xur8

"My trusty Shifter"

Hmmmmm............. I am trying to imagine what a shifter (Australian) is in this context. Oh, I imagine its a wrench (English) of some kind, but one can never be perfectly certain of these things when the other party is speaking a foreign language. Australia and the United States: two countries separated by a common language. I like that, I think I'll publish it in my book of quotes.

I guess we will get the equivalent English word for a "shifter", but I am almost afraid to ask. Please don't tell us that it is Australian for "slip-joint pliers" I don't think I could stand the shock!

.............F>

Angst, GA.

Reply to
Froggy

A simple sheet metal 'retainer' cover plate can be placed over the T-nut to hold it in place. A large 'Fender Washer' with a couple mounting holes drilled into it will work.

But a threaded insert is a better solution, and hardly any more work.

Dan Mitchell ==========

"Stuart D." wrote:

Reply to
Daniel A. Mitchell

The lag screws are nice since they produce a LOT more vertical height adjustment for a given rotation (coarser thread). We use these on out clubs modular layout, but we have had some problem with the screws splitting the wooden mounting blocks. If you drill the hole too large, the screws strip. If you drill them smaller, they sometimes split the blocks. It's *NOT* a big problem, and easily corrected by gluing the block back together. I don't recall that we've ever had a glued block split again in the same location.

Dan Mitchell ==========

Tra>

Reply to
Daniel A. Mitchell

Think about it. It is actually less work. Drill Screw Through (finished, done, d'ende, fini, voila, finalé)

Not subject to swelling and shrinking of the wood, immune to rough handling, won't shake or wobble loose and precision hole size not important, anything "close" will do OK.

Not that I'd EVER suggest that "close" was good enough, one should always use the correct drill, but you know what I mean.

Reply to
Froggy

Oops, barrel bolts and threaded inserts are not the same thing

This is a barrel bolt

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This is a threaded insert:

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Actually there are many different kinds of threaded inserts, but this is like the ones I use. Some are hex-drive and some are installed with a screwdriver.

There are also barrel nuts, which is what I think Larry meant to type, but they are very similar to T-nuts and are used much the same way

This is a barrel nut

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Reply to
Froggy

adjusted with

context.

"slip-joint pliers"

I don't know if "shifter" is the Australian term for what we in the US call a "wrench," but isn't "spanner" the UK term for "wrench?"

-- Bill McC.

Reply to
Bill McCutcheon

Actually, what I was talking about was a cross dowel. See:

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For some reason, I've always called those barrel bolts :-).

BYW, there are also T-nuts with wings that have screw holes in them to keep them from pulling out.

Reply to
Larry Blanchard

Yeah, those would work, although you'd have to drill two holes instead of one and they'd get loose and wobbly after a very short time when being used to hold the adjustable feet. Getting them to work just right would mean very tight control of hole diameter and position.

Easy to see why. No doubt there are many who do likewise.

Quite true. A function of the never-ending quest to build a better, less expensive mouse trap.

Ah, but the threaded insert is still the king of the hill as it requires only one hole be drilled, which hole does not require precise sizing or positioning, AND it requires no auxiliary support devices, glues, screws or mechanisms to ensure its reliability; PLUS it cannot come loose, get stripped, wobble, get misaligned or be misplaced.

It is as perfect a solution to the adjustable table height function as the cutting off of the glad hand is to the pesky magnetic coupler issue.

.............F>

VBG, GA

Reply to
Froggy

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