Hold down choices..

[wcarrothers1]

Ok... Trying to figure the best way to design the table/hold downs and such for my machine...

The plan was to double up 3/4mfd so I would end up only replaceing the top on a regular basis.. I already have Gcode to drill the holes and countersync's so I can pretty quick make a new aligned top and secure it quick.. Was thinking about making another program to lay out holes to use those hammer steel T - nut things http://woodworker.com/cgi-bin/FULLPR...2&LARGEVIEW=ON

Or something like that...

Now the problem in my head is... if I should sandwitch the T nut in between the 2 boards or at the bottom of the second (see pic)

Countersync one of those between would be a pain in the but in my mind. A lot of extra work. Perhaps put the counter sync in the top of the bottom board to give space fot he T nut (way 3 ).. rather then in the bottom of the top board (way 1)

Way 2 would probably be the easyier then all since you would just have to put the new top board on and run the redrill program to line everything up.. But we all know those T nuts would end up falling out the bottom (so they would need glued in or a backer board put on each) + way 2 would prevent laying out the T nuts in areas where I have the support bars running supporting the bottom board..

Maybe there is some other better way out there.

I think I'm leaning toward Tnut in the bottom of the top board with an area in the bottom board counter sunk so the Tnut will have room..

Anywho..

b.

[Rance]

b,

How bout 'way 3' but with the T-nut turned upside down with it's teeth biting into the bottom board. I know, I know, that's pulling against the T-nut in the wrong direction when you actually use them. However, it makes the fabricating of a new top board (your sacrificial board) much easier since you have no counter-sinking or transferring T-nuts from the old one to the new one. Just a thought.

Rance

[wcarrothers1]

Rance.. That does sound like a good idea... Although when fabing the new board going to have to be carefull while re-drilling the holes (not to go to deep or have some sort of spacer board during the process.

Sounds like a good idea. Then I could also glue them in.

b./

[Geof]

A problem with the T nuts is they are very soft metal and will gall or strip easily. If you have them sandwiched it will be difficult to replace a damaged one.

An alternative is to use the threaded inserts designed for screwing into mdf. These have a large knife edge thread on the OD and are tapped 10-24 or 1/4-20 inside with a length of about 1/2" - 5/8". They insert from the top so they can be replaced easily.

[Madclicker]

Originally Posted by Geof A problem with the T nuts is they are very soft metal and will gall or strip easily. If you have them sandwiched it will be difficult to replace a damaged one. An alternative is to use the threaded inserts designed for screwing into mdf. These have a large knife edge thread on the OD and are tapped 10-24 or 1/4-20 inside with a length of about 1/2" - 5/8". They insert from the top so they can be replaced easily.

And extracted and re-used.

[Normsthename]

How bout 'way 3' but with the T-nut turned upside down with it's teeth biting into the bottom board. I know, I know, that's pulling against the T-nut in the wrong direction when you actually use them. However, it makes the fabricating of a new top board (your sacrificial board) much easier since you have no counter-sinking or transferring T-nuts from the old one to the new one. Just a thought.

I am using M8 T-Nuts on my Router.
I have 2 x 18mm MDF sheets for the bed, with the top one being a sacrificial one.
I drill a 8mm Hole thru' the two sheets where I want the clamp locating, and then put the M8 Bolt thru'. with a metal plate to spread the load.
Fit the T-Nut underneath on the Bolt and tighten the bolt to pull the T-Nut into the MDF
I then use a plate approx. 50mm x 15mm x 6mm with a hole in centre to clamp wood down, and I use a packer slightly thicker than the actual wood I am routing, this puts more pressure on the work piece.

I have not had any problems so far, and they clamp the parts down quickly and nicely.
Care must be taken not to overtighten the bolt or you would strip the T-Nut, they hold the wood very securely even at quite low torque on the M8 Bolts.
I have about 8 T-Nuts fitted in my Router bed so far and they cater for most sizes of wood.
If I need a new position I just fit a new T-Nut in that location.

Andy