Homemade Knurled Inserts

[Onoff]

I have a fairly immediate need of 6 knurled inserts in stainless to take an M12 bolt. To be resin fixed into brickwork. Not particularly structurally critical, the bolts will be in shear. The brickwork will be drilled carefully, (non hammer) with a grit edged hole saw, 2mm oversize, then the insert resin fixed in.

Something like this but I don't want to really a) wait and b) pay £7.36 each. These are allegedly M12x25 to go in a 22 mm hole a typo I presume, they must I guess be made from M20 stud.

I can likely find some M16 stainless studding here, I've certainly no M20 or M24.

I can probably get access to the BiL's lathe. So centre drill, drill out to 10.2mm...think I have a drill, 10.5 if not, then tap at M12.

Doable or am I on a hiding to nothing? Is the resultant, remaining thin wall, likely to collapse on me when tapping?

The far simpler, resin fixed (and thus projecting) studding is an option I'd rather avoid as a I want to possible remove the frame being fixed later on.

 

[Morrisman]

I can’t see a problem making them. I’d tap each one in turn before cutting it off the rod, so you can get a good grip in vice, with soft jaws and not potentially squish it.

 

[Agroshield]

Studding is likely to be made using a thread rolling process. That will work harden the material and make it more challenging to drill and tap than the equivalent A2 or A4 plain bar.

I would start with plain bar, drill and tap M12 and then add your own 'knurl' using a grinder. The random nature of the artisan-made pattern will aid in stress distribution.

For an M12 female thread in stainless, I would look carefully at a coupling nut (Screwfix 5565G). Again, grind some grooves into the points or screwcut a very coarse (left and right hand) thread on the outside.

 

[Kram]

M16 rod will only give you 1mm wall between the threads, it can be done on a lathe but not ideal.

Larger bar needs a bigger hole.

What is it for? 12mm rawl plugs and coach screws may work?

3d print a thread to be resin fixed in?

 

[Onoff]

What is it for? 12mm rawl plugs and coach screws may work?

3d print a thread to be resin fixed in?

I'm loathe to put pictures up on the open web as it's ref house / security. I was actually thinking PETG copies of the inserts.

Do you reckon threaded or knurled external faces?

Wonder if the resin will react with the PETG?

 

[Nomad]

Would expanding metal rawl plugs work for you?

Assuming the head of the bolt will be covered when fitted (or use tamper proof bolts) it's fairly secure and flush when removed.

 

[Onoff]

Would expanding metal rawl plugs work for you?

Assuming the head of the bolt will be covered when fitted (or use tamper proof bolts) it's fairly secure and flush when removed.
View attachment 478453

No. I don't want any expansion loads on the bricks so it has to be resin. If using a stud I'd have fitted a mesh sleeve.

Just to complicate things it has to go into these "hollow" bricks (one shown where I sliced a slip off of it as I can't find an intact one):

 

[Morrisman]

With holes that big you might find the epoxy slowly dribbles out, before it even starts to harden up. I’ve done similar and put masking tape around the stud to keep the epoxy in.

 

[Onoff]

My mistake! The fixing holes in the frame are for M10 not M12. Thinking now to use tarmac type fixings and maybe drop to M8 with a big penny washer.

Got as far as drilling using a cheap as, 11mm masonry bit (that's now blunt) as that's the hole size in the frame. Some holes are on the edge of the brick, some dead centre, some on the brick edge:

The pain is the fixings are into these hollow bricks which I'd forgotten. Haven't got a complete brick left, just this one I cut for a slip:

Reckons this could be the way to go:

Now thinking TPU...

 

[Agroshield]

3d print a thread to be resin fixed in?

That is a very good idea. The big advantage is that on a 3D model, you can make the external thread the same pitch (1.75mm) as the internal one and also clock the two threads so the largest diameter of the internal one coincides with the largest diameter of the external one. You can thus minimise the thickness - effectively a sheath or condom for the male thread of the bolt so it does not contact the resin.

Reckons this could be the way to go:

Any fixings with rubber on them will exert some expansive force on the bricks, which you said you did not want.

 

[Onoff]

Any fixings with rubber on them will exert some expansive force on the bricks, which you said you did not want.

True. Though tbh how much compared to say a metal expanding anchor?

As aforementioned it's actually M10 not M12 I've realised.

 

[Agroshield]

True. Though tbh how much compared to say a metal expanding anchor?

It would be more gentle and more spread out than a metal one (which would concentrate a large load onto a small area).

The thing is, would the rubber squidge out into the holes of the brick?

Could you do a test run in a spare brick (non-hammer drilled) and look at what happens when you tighen it and assess whether it is OK to carry the load.

If you had time, maybe you could drill the hole, spray some crazy foam into it to fill any voids and then insert the anchor 24h later. Be sure to protect the external face of the brick in case the foam tries to escape.

 

[Onoff]

If you had time, maybe you could drill the hole, spray some crazy foam into it to fill any voids and then insert the anchor 24h later.

"That's a cracking idea Gromit!"

Currently printing a test insert in black PETG. M18 externally, M10 internal. An integral 5mm washer to keep the frame off the wall a tad.

The worry now is the exothermic reaction temperature of the resin vs the PETG's glass transition temperature which is circa 60 to 90⁰C. ASA and ABS are options here...

 

[Agroshield]

The worry now is the exothermic reaction temperature of the resin...

I am wondering if while it is curing, you can screw something metallic into the insert. That will conduct some of the heat away.

Is there any benfit to cooling the resin down in the fridge? That will slow down its curing time for sure, but would it also reduce the highest temperature seen while curing?

 

[Kram]

Is the problem with studs is the other end of the frame might not have clearance to be withdrawn?

I would say drill many 4mm holes in the frame and affix with timber screws and 6mm rawlplugs in the brick. The weak point is the brick, many 5mm screws will be stronger than three or four 10mm bolts. Also quicker to drill.

Option instead of rawlplugs, squirt anchor or epoxy resin in there, let set and pilot dril 2.5mm. Use screws that have a self tapping /piloting wood screws.

 

[Onoff]

So 20mm hole in the brickwork. Then insert this, black PETG, M18 external thread with an M10 internal thread for the bolts. Inbuilt washer to keep the frame away from the brick a tad:

 

[Onoff]

Fingers crossed!

https://flic.kr/p/2qCFAYy

https://flic.kr/p/2qCGPpa

 

[Agroshield]

Blutak/silicone/sellotape the open end (the end inside the wall) else when you push it in, the resin will go up the M10 hole.

 

[Morrisman]

You’ll also need to see what sort of air space you’ve drilled into, and adjust the amount of epoxy to suit.

 

[Onoff]

You’ll also need to see what sort of air space you’ve drilled into, and adjust the amount of epoxy to suit.

Going to be tricky to tell due to an unknown amount of mortar above and below the brick. At worst I reckon I'll have to fill up one circular pocket / hollow, maybe two if I've penetrated the centre divider:

A little 3D printed, rotating centre, so I can line up the 20mm dia carbide grit hole saw on the already drilled 11mm hole: