TromboneChat

Has anyone cracked how to separate these as I'm having problems holding the Cup to prevent it from
moving in my hands......

If anyone can help at all.. I was considering getting some super grip thick rubber and wrapping it around
the cup whilst spannering the flats of the shank ?

Impact, not brute force. Put a wrench on the hex and hit the other end of the wrench to turn with a little impact. Box-end wrench works best. 9/16 is the correct size; 14mm also works.

Light bonks does wonders. I usually hold the shank and tap the cup on my desk pad in the direction of rotation.

Yup, I’ve had a few of mine stuck. I always just firmly tap it with a rawhide mallet until it is loose enough for a wrench to take the two apart. Hasn’t failed me yet.

Get a small strap wrench to help you get a grip on the round parts (rims/cups).

would graphite powder work as a preventative you think?

A little lesson in mechanics:
A thread is a circular wedge, forcing two flat parts together - the top of the shank and the bottom.of the cup.
Friction keeps them together. That's friction in the thread itself AND friction of the two mating surfaces. If you lubricate the threads it allows it to tighten more, and does not necessarily make it easier to get apart.

Impact or vibration breaks the bond far better and easier than brute force.

A big thank you to you All for your contributions. As this is Doug's set up, I will try his suggestion which I'm hoping will sort my Issue, if I struggle a little, I have a few back up options,

This is why I love this forum.

Toodle Pip chaps !

Yes, follow Doug's advice.
Tried it once, worked wonders, no damaged part.

With other systems, there is a huge risk of damaging the parts and you do not want that.

Does anyone have a recommendation for a specific brand / type of rawhide mallet to use? My DE mouthpieces are currently all able to be unscrewed, but I know that eventually one is going to get a little stuck.

Rawhide mallets tend to be expensive, but a cheap wood crab mallet from a grocery store does just as well

Success ! I've managed to separate these guys, I tapped the Cup and shank gently a few times, held the Hex with the wrench in my left hand but put a blue latex rubber clove on my right hand, gently gripped the Cup and twisted anticlockwise and it unlocked.

I'm pretty sure the slight tapping prior must have dislodged it a bit as it unscrewed pretty much straight away.

Few ! Thanks everyone

I always have appreciated that you can create a custom mouthpiece with Doug's modular system, and when you go for a big change like changing the rim size, it's so cool. Hopefully that's why the OP is having to separate the parts. Or if you need to switch to lexan for an outdoor event in the freezing cold.

But I knew a guy who bought a single rim and used it on multiple setups -- like 4 mouthpiece bottoms. I was like, my guy, buy a second rim.

I use a wrench and the underside of a standard mousepad. I'll use the mousepad for anything that needs tightening/loosening, like jar lids, some light plumbing work, working on the car.