Making a nut bigger?

[Infraviolet]

Here's an interesting problem.

I'm tightening an M6 bolt in to a nut, and doing it up very tight indeed so it can clamp an object. The trouble is that the mount the bolt an nut go it to is 3d printed, and when the bolt/nut start getting fairly tight the nut rips its way through the plastic hex shaped nut sink structure which has been created in the 3d printed part for it to sit in. What was a hex shaped hole in the part gets rounded out by the nut preferring to turn and tear slowly through plastic than be tightened any further.

If the nut were somewhat bigger, then the hex would be against mroe plastic and wouldn't be able to tear through so easily. But an M6 nut is an M6 nut and the outside dimensions are always the same. I've certainly never seen M6 nuts on sale with, say, double sized outer hex measurements.

Any thoughts on ways to "make the nut bigger" and thereby stop it tearing its hex shaped hole in a 3d printed part in to a round hole it can turn within? The printed part is standing up to the compression forces of the claping and everthing just fine, so if I can just stop the nut grinding away its own hole's hex then I'd have everything working.

Here's a picture of an example of a nut sink in a printed part, so my meaning about rouding out is clear:
https://content.instructables.com/ORIG/F51/LTMP/IAZ70GN3/F51LTMPIAZ70GN3.jpg

Thanks

[Warpspeed]

Use a nut plate.
Many types commercially available, or you could make your own.
https://www.google.com/search?q=nut+plate&hl=en&gl=ar&tbm=isch&source=hp&biw=1623&bih=909&ei=yDIyY-WwDrjv4-EPmb6H6A0&iflsig=AJiK0e8AAAAAYzJA2Opf80eN1zqlVl7G3-_RWekwxtoc&ved=0ahUKEwjltP-6y7P6AhW49zgGHRnfAd0Q4dUDCAY&uact=5&oq=nut+plate&gs_lcp=CgNpbWcQAzIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBggAEB4QBTIGCAAQHhAFMgYIABAeEAU6CAgAEIAEELEDOgQIABADOgsIABCABBCxAxCDAVCCC1ilIGCOJGgAcAB4AIABe4gBvAiSAQMwLjmYAQCgAQGqAQtnd3Mtd2l6LWltZ7ABAA&sclient=img

[Ian.M]

A square nut may be easier to find and would be far more resistant to wallowing out the hole it sits in: https://www.google.co.uk/search?q=m6+square+nut&tbm=isch

If that's not enough, consider switching to a cross-dowel (aka barrel) nut: https://www.google.co.uk/search?q=m6+dowel+nut&tbm=isch but they are more of a PITA as you need to check the dowel is rotated to align the cross hole.

[David Hess]

Metric tee nuts are available.

[hubi]

I think the problem is the nyloc nut. Try a regular nut and Loctite blue.

[thm_w]

I think the problem is the nyloc nut. Try a regular nut and Loctite blue.

Yeah the nyloc takes a fair amount of torque.

In this case, does it matter if the fastener spins? Probably not, you have the nyloc already, so get rid of the hex walls and use a socket to tighten it instead.
Or use threadlock and your original 3D printed design, as hubi says.

[AndyBeez]

Another approach, let the nut 'turn' by clamping down on a 'penny' washer mounted on the block. The fastening force is downward through the washer onto the block, and not a twisting moment wrecking the plastic. Would require a redesign of the part - and a small spanner. Normally this part would be made for industry from hard polycarbonate. 3d printed polyamide/PA might not be strong enough.

[Zeyneb]

You can also make your own custom shaped nut.

How: buy steel profile in the shape that is suitable to fit into your 3d printed design and drill a hole and tap that hole.

[CatalinaWOW]

Another approach that might work is to modify your 3D print to have rectangular metal braces across two flats of the hole.  The rectangular chunks are easy to make or even buy and could be glued into their channels or with some finicky design set up to snap into their holes.

Large volume purchasers have no problem getting custom nuts and/or bolts with a very modest price premium, but such options aren't open to low volume orders.  You can sometimes find an appropriate product at overstock sites, but it is very hit or miss.