[loud3803]

I was testing some fasteners for MDF/Partical board and came up with some very interesting results most noteably with thread inserts. I was using a thread insert from Mcmaster-Carr part # 92105A100.
My Results were as follows:

Partical Board 3/4" thick x1"x1" Face pull force 403 lbf, end pull force 270 lbf: MDF 3/4" thick x1"x1" Face pull force 108 lbf end pull force 225 lbf.

The results for the 1/4"-20 threded directly into the wood 3/4" are as follows:

Partical Board 3/4"x1x1 Face 370 lbf End 299 lbf.
MDF 3/4"x1x1 Face 139 lbf End 295 lbf.


I noticed that many of the hobby cnc plans call for threads tapped directly into the MDF, I was worried about the strength of this so I ran my tests and found that if you don't plan on taking it apart, threading directly into the wood isn't a big deal.


These tests were run on an Admet pull/compression testing machine.

Louis

[Geof]

You don't say what size the inserts were but as you compared them with 1/4-20 I guess they were 1/4-20.

Your face results are almost the same as I found in similar testing.

Here is a slight extension to your test which I found may a significant difference. Countebore the pilot hole for the insert to the insert OD size for a depth of about 0.10".

What I observed happening with the insert just screwed into the pilot hole was that a crack in the surface of the mdf would start at the point where the OD thread on the insert cut its way into the hole; then the insert would pull out slightly sideways.

With the counterbore the entry cut is below the surface of the mdf and a crack does not start at the entry point. The insert pulls out straight up and the retention is at least 30% stronger.

[loud3803]

I guess I should have posted the specs:

Type
Self-Tapping

Self-Tapping Type
Knife-Thread Hex Drive with Flange

For Use With
Wood

Application
Create New Threads

Material
Steel

Steel Type
Die Cast Zinc-Alloy

Finish/Coating
Plain

System of Measurement
Inch

Internal Thread Size
1/4"-20

Internal Thread Fit
2B

Insert Length
33/64"

Drill Size
23/64"

Hex Key
M6

Flange Thickness
.010" - .020"

These are the same inserts that are used on occasion in RTA Furniture.

[Geof]

You contradict yourself a little; Die Cast Zinc alloy is not a type of steel it is a Zinc alloy.

The inserts I tested were the pretty close to the same OD and length and had the knife style thread but they did not have a flange and used a screwdriver slot for inserting. These were made out of steel, leaded steel was my guess because I faced some off to test a shorter length and they machined just like leaded steel.

I had some of the zinc alloy ones but did not use them because my application involved frequent disassembly and the zinc alloy was just too soft and chewed away.

[loud3803]

That was a direct paste from Mcmaster-Carr, I saw it too but I was to lazy to change it.

[Geof]

Now that does give you a lot of faith in the reliability of their information.

[LaserImage]

A little bit of CA glue will make those threads a bit stronger and allow you to take it apart and reassemble. I would be curious to see what CA would do to your tests.

Gary

[loud3803]

I'll have to look into that. I was thinking about that, that is how I mount engines on model airplanes instead of using blind nuts, saves on weight.

Louis

[wjfiles]

Anyone used T-NUTS.
They will not pull out.
WJF