Disks Under Centennial Rails

C

Chip Roberson

AzB Silver Member
Silver Member
The metal disks that the 3/8-16 bolt goes into from underside of the rail. The screws that hold the disk in place are loose in many spots. I can turn some of the disks and then drill new holes to take care of the problem, but there are a few that have been turned many times already and that could cause the problem to arise again , wanting to nip this problem before it goes further. Either I can use some glue in the screw holes, or ( Being a hardware supplier to the Furniture Companies) I can use a threaded insert from Stafast that use the existing holes and then go with a 5/16-18 machine screw to hold the disks in,,,,seems like this table has been around. I know they were tight when I installed it back years ago,,always something to come up and bite ya . I'm thinking of using the inserts ,,Hmmm
 
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Yeah that would work. The only problem I see with the machine screws to hold the round disc in place is that you will need to use loctite, or inserts with a locking feature, otherwise you will be taking the rails off to retighten periodically. The big rail bolts use the domed washers to help keep them tight, and they are easily accessed, but your machine screws wouldn’t be so easy to retighten.

The rail experts usually just ditch those figure 8s, or round plates, and go with a big hardwood insert. If you do a search you can find the specs on that insert, I don’t have that one bookmarked.

Another fix for those is to drive a hardwood splinter down the stripped out hole and glue in with Elmers wood glue, cut off the excess and she is good to go.
 
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Chip Roberson said:
The metal disks that the 3/8-16 bolt goes into from underside of the rail. The screws that hold the disk in place are loose in many spots. I can turn some of the disks and then drill new holes to take care of the problem, but there are a few that have been turned many times already and that could cause the problem to arise again , wanting to nip this problem before it goes further. Either I can use some glue in the screw holes, or ( Being a hardware supplier to the Furniture Companies) I can use a threaded insert from Stafast that use the existing holes and then go with a 5/16-18 machine screw to hold the disks in,,,,seems like this table has been around. I know they were tight when I installed it back years ago,,always something to come up and bite ya . I'm thinking of using the inserts ,,Hmmm
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I put wooden dowels in the holes, and tighten the wood screws.

If you are planning to use the Stafast inserts, I might recommend eliminating the plates entirely, and using a single 3/8" insert.
 
Not qualified to say if they will work in pool table rails; however i sometimes make and use sort of SK type (hex socket) for furniture and millwork apps. Except i use machine thread OD, & actually tap the wood part with a tapping head. Wood fiber springs, so the thread size is usually quite tight. Or i can adjust the threaded part OD on the turret lathe when running them to be a tight fit in a given tapped hole. If an insert is loose, a little thin ca wicked in from the back after assembly can fix it. My largest geometric die head is a 9/16", so the inserts made in bulk are 1/2" OD or less, though.

No doubt if you've sold a ton of them, you know where the data pages are for shear strength in the wood, or fastener pull out yield force directly, with threads parallel with wood grain. It has to be (almost literally) tons more for a .728" OD thread at least say 9/16" into hardwood, compared with existing, what, 3ea #10 screws? (You can tell i don't really know what size goes in those plates, but have seen the pictures & it is not inspiring. :) ) Of course the deeper the insert can be, the better.

smt
 
Ssonerai said:
Except i use machine thread OD, & actually tap the wood part with a tapping head.
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If you do this, why wouldn't you, in the case of Brunswick Anniversary or Gold Crown rails, just tap the wood for the 3/8-16 machine thread of the rail retaining bolt? Why didn't Brunswick just tap the wood for this thread instead of going through the trouble of the round or figure-eight nut plates?

The reason is that machine threads are not appropriate to hardwood material. One needs a deeper thread profile to hold in wood, like, for example, a wood screw thread. If there wasn't a difference in thread profile requirements for wood and metal, inserts wouldn't exist.

There are plenty of threaded inserts available that are designed to be screwed into hardwood and provide machine threads.

I agree with Geoff, that if using an insert, just use a single one in place of the nut plate that has 3/8-16 internal threads. If you're really fussy, make some hardwood disks to glue in and fill the mortise for the nut plate.
 
Thanks for all the responses , little history to add towards fasteners ,,The furniture industry gave up on wood screws back in the early 60's because of a couple of things, 1 the threads were tapered and 2 they were slot head instead of phillips head. The twinfast screws then came around and were used until the late 1980's and they were replaced with the best wood screw fastener ever the Deep Thread. Large threads on thin body that cuts into the wood and holds. Unless you have them special made the sizes don't go over a 10. The insert I will use has the deep thread characteristics mentioned. I would use the blue loctite to ensure the machine screws would not back out and I'm thinking of going one step further,,after cleaning everything up well , lay a thick layer of Barge glue to both the disk and the wood let it be for the curing time then insert the disk and screw down . Thinking the contact cement could also act like a shock absorber
 
If you do this, why wouldn't you, in the case of Brunswick Anniversary or Gold Crown rails, just tap the wood for the 3/8-16 machine thread of the rail retaining bolt? Why didn't Brunswick just tap the wood for this thread instead of going through the trouble of the round or figure-eight nut plates?
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I take it you are being rhetorical in order to set up the explanation.
However, to address it with some other points:

1.) with threads essentially parallel with the wood grain (as opposed to going into end grain hence cutting across all the fibers) increasing diameter makes a rapid very large improvement in pull-out force required. So the 3/8" machine screw fastener into the .720 (or so) dia insert acts like a .720 dia bolt as far as when/whether the wood fails.

2.) inserts are usually used for KD assembly. The threads wear out faster in wood than in a compatible metal, also over the service life of the article (say a pool table) the metal part is sacrificial/can be replaced.

3.) (minor point) it is probably less likely for most people to torque out the threads in a metallic nut than in some wood sections or types. The insert gives (as per 1.) above) can give over twice the withdrawal force of the actual bolt size in wood for the same penetration.

No-tap fasteners are an installation improvement, not necessarily a significant strength enhancement over threaded coarse machine thread inserts of the same diameter. IOW they obviate the tapping step. I sometimes make and use tapped systems because the fastener can more reliably be placed in locations that might split with the no-tap type. Including plywood where the no-tap insert can sort of spread the grain/"swell" the panel near an edge including leading to visible splits from the edge view. OTOH where knife edge version of no-tap fasteners can be used (as probably in pool table rails) they will most likely attain the ultimate possible for a given diameter.

AFA Brunswick and the figure 8 plates, i have always wondered that. Why? inserts could be so much stronger and at the factory level have to be faster to install with machines.

smt

PS, will be curious to learn if your barge cement experiment gives any improvement. Properly used, filled epoxy could. But fundamentally the figure 8 design is just a poor one for a connector that sees significant static and dynamic loads as a matter of normal function. Or another way to put it, in that installation they have proven to be too slight in terms of attachment details.
 
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Ssonerai said:
AFA Brunswick and the figure 8 plates, i have always wondered that. Why? inserts could be so much stronger and at the factory level have to be faster to install with machines.
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I believe the plate design started in the 1940's. However, they changed over to inserts in the late 70's.
 
bradsh98 said:
I believe the plate design started in the 1940's. However, they changed over to inserts in the late 70's.
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Is the floating nut plate considered an "insert". Diamond uses threaded inserts from the factory. I don't think Brunswick has but I could be wrong.
 
rexus31 said:
Is the floating nut plate considered an "insert". Diamond uses threaded inserts from the factory. I don't think Brunswick has but I could be wrong.
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Brunswick started using flanged tapping inserts on the Gold Crown III, back in the 70's. They are used for holding the skirts and pocket castings in place (They are the super cheap style, and are prone to failure). For the rail bolts, they used the captured nut plate.

92105A430p1-b01-digitall@1x_636849197688854971.png


I don't know what Brunswick uses on the newer tables. I've never seen anything newer than a Gold Crown IV.
 
bradsh98 said:
Brunswick started using flanged tapping inserts on the Gold Crown III, back in the 70's. They are used for holding the skirts and pocket castings in place (They are the super cheap style, and are prone to failure). For the rail bolts, they used the captured nut plate.

92105A430p1-b01-digitall@1x_636849197688854971.png


I don't know what Brunswick uses on the newer tables. I've never seen anything newer than a Gold Crown IV.
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Thanks for the clarification. I had rail bolts and fasteners on the brain.
 
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