Engineering question : Max torque of bolt into 10mm 5083 aluminium plate?

[Plevier]

Bit of thread drift here but a genuine question.
On my boat (Dehler) all the deck gear is fastened by bolts into tapped aluminium plates bonded into the structure.
This includes the size 42 genoa winches. They are bolted to ali plates 180mm dia x 8mm thick (I have the factory drawing). There are no nuts underneath; you can see the bolt ends coming through into the locker.
The implication of this thread is that the fixing bolts for them should be barely nipped up for fear of stripping the plate!
Really?

 

[wipe_out]

Bit of thread drift here but a genuine question.
On my boat (Dehler) all the deck gear is fastened by bolts into tapped aluminium plates bonded into the structure.
This includes the size 42 genoa winches. They are bolted to ali plates 180mm dia x 8mm thick (I have the factory drawing). There are no nuts underneath; you can see the bolt ends coming through into the locker.
The implication of this thread is that the fixing bolts for them should be barely nipped up for fear of stripping the plate!
Really?

I would imagine that the winches have more of a lateral force on them than a vertical force (relatively speaking).. So it's probably using the sheer strength of the fixings rather than the force they are being held down with.. Of course if you can see the bolts coming through there is nothing stopping you fitting nuts for extra strength, or just peace or mind..

 

[Avocet]

Yes, it's a very different load case. In the gasket one, he's using the bolts in pure tension to create a clamping force on a gasket. With the winch, because the rope is pulling on it at some height above the mountings, there will be a bending moment as well as pure shear loads (which will act to try and "uproot" the bolts on the opposite side to where the rope is pulling, but that won't be much of a force.

 

[prof pat pending]

Hi,

Hoping someone has some idea on this..

I have to put M8 bolts into 10mm thick 5083 aluminium.. The aluminium plate has M8 holes drilled and tapped into it..

Anyone have any idea what torque the bolts would take before I risk striping the threads on the plate?

Here you go http://www.futek.com/boltcalc.aspx?mode=metric

Go with the 6061 for the mating material. It has a slightly higher yield strength, but it’s the nearest one.

Something else to consider is what material the bolts are made of?

 

[wipe_out]

Here you go http://www.futek.com/boltcalc.aspx?mode=metric

Go with the 6061 for the mating material. It has a slightly higher yield strength, but it’s the nearest one.

Something else to consider is what material the bolts are made of?

Interesting and probably the closest calculator to my needs.. It says 13.773 ft-lb recommended and 18.364 ft-lb maximum so if I went to 10 ft-lb I guess it would be "safe"!?!?..

Bolts will be stainless steel and planning on using Loctite 243 in the threads which will hold up against the petrol in the tank.. Other option was Loctite 572 sealer but I think I need the thread locking since the torque is quite low.. Maybe use the 572 on the bolt head flange as a seal..

 

[wipe_out]

Looked up the poof strength of the 5083 Ali (240MPa) and used the calculator.. Gave a slightly lower result than 6061.. 11.932 ft-lb recommended and 15.91 ft-lb maximum.. So 10 ft-lb should be fine as a proposed torque (maybe)..

 

[prof pat pending]

Sounds fair to me :encouragement:

There is a potential corrosion risk mixing stainless and aluminium, but it shouldn't be an issue in that application

 

[gordmac]

Hi,

Hoping someone has some idea on this..

I have to put M8 bolts into 10mm thick 5083 aluminium.. The aluminium plate has M8 holes drilled and tapped into it..

Anyone have any idea what torque the bolts would take before I risk striping the threads on the plate?

Engineering answer, don't do it that way!
Not sure I get the arrangement, are you putting 10mm thick panels on to a 10mm thick tank that has M8 threads through it? You may be better screwing M8 setscrews into the threaded holes to make studs, less likely to strip the threads that way.

 

[wipe_out]

Engineering answer, don't do it that way!
Not sure I get the arrangement, are you putting 10mm thick panels on to a 10mm thick tank that has M8 threads through it? You may be better screwing M8 setscrews into the threaded holes to make studs, less likely to strip the threads that way.

Not quite..

Tank is plastic, about 5mm thick.. A 10mm aluminium plate inside the tank with a 3mm rubber gasket, inner plate has 38 x M8 threaded holes 50mm apart.. Then another 3mm gasket and 10mm ali plate with clearance holes on the outside of the tank to bolt through.. Hatch cover is 580mm x 440mm..

 

[alahol2]

Tank is plastic, about 5mm thick.. A 10mm aluminium plate inside the tank with a 3mm rubber gasket, inner plate has 38 x M8 threaded holes 50mm apart.. Then another 3mm gasket and 10mm ali plate with clearance holes on the outside of the tank to bolt through.. Hatch cover is 580mm x 440mm..

Personally I think I would use machine screws, screw them fully into the inner plate with Loctite to produce a set of 'studs' (maybe fibre washers?), then use washers and nuts on the outside.

 

[john_morris_uk]

Here you go http://www.futek.com/boltcalc.aspx?mode=metric

Brilliant site. Thank you.

 

[wipe_out]

Personally I think I would use machine screws, screw them fully into the inner plate with Loctite to produce a set of 'studs' (maybe fibre washers?), then use washers and nuts on the outside.

Yes, that is an option but will mean the machine screws have to somehow be fitted to the inner plate while it's in the tank.. The plate won't go through with the "studs" already in place which makes that option a little tricky..

Since it's all been made already I will try bolting from the top with 10 ft-lb of torque and will then try and pressurise the tank with air and see if it holds.. If not I will have to attempt fitting machine screws from the inside so I can pull it down harder..

If none of this works it will mean a new tank which is going to be expensive and mean I miss even more of the season so I am hoping it works on the first attempt..

 

[gordmac]

Do you actually need the holes? How about welding a plastic plate over them? Studs is the way to do it, how do you hold the inside plate in place to get the screws to start?

 

[wipe_out]

Do you actually need the holes? How about welding a plastic plate over them? Studs is the way to do it, how do you hold the inside plate in place to get the screws to start?

The tank is made is a nylon and it didn't appear that plastic welding would work and be structurally strong from what I looked up..

Holding the inside plate to start is also a bit of trickery..

One option is to use a small m4 or m6 countersunk machine screw (countersunk into the plastic tank) on each side to hold the bottom plate in place..
The more of a "hack" solution is to suspend it with a bit of fishing line through a couple of the holes on each side, then get the first bolts started through the top plate and pull the fishing line out..

 

[john_morris_uk]

The tank is made is a nylon and it didn't appear that plastic welding would work and be structurally strong from what I looked up..

Holding the inside plate to start is also a bit of trickery..

The more of a "hack" solution is to suspend it with a bit of fishing line through a couple of the holes on each side, then get the first bolts started through the top plate and pull the fishing line out..

If you choose the "hack" solution, I hope you're not in earshot of anyone removing the inspection plate!

 

[prof pat pending]

I agree that studs are the way to go here

For the installation issue, I'd modify 4 of the studs with a small hole down the middle (not all the way through) and braze a length of wire into each hole.
Assemble as many studs as possible into the inner plate whilst it’s in the tank with the 4 wires poking out of the holes in the tank (inner gasket in place)
Add the upper gasket, the upper plate and 4 nuts and then pull up on the wires to bring the inner section into place. Spin the 4 nuts onto the threads and all will be loosely held in place while you add the other nuts.
Any studs that cant be fitted in stage 1 can be added using 2 thin nuts locked onto the thread to screw them in.

A smear of Dow Corning Silastic on the upper gasket will help your sealing worries.
This is a silicone type sealer and is fuel proof

Cut the wires off when you are happy everything is seated correctly.

PS...reading back through your posts, don't use a heat source in a fuel tank unless you are absolutely certain there is no fuel in the vicinity

 

[wipe_out]

A smear of Dow Corning Silastic on the upper gasket will help your sealing worries.
This is a silicone type sealer and is fuel proof

Which of the Dow Corning products is specifically petrol proof? When I looked previously (not at Dow Corning admittedly) I couldn't find any petrol proof sealants.. When reading the spec sheets, those that mentioned petrol had very limited resistance..

 

[prof pat pending]

iirc all of the Silastic range are fuel proof

 

[prof pat pending]

Try this

http://www.dowcorning.com/applicati...DCCD=PRODUCT&WT.svl=1&DCCT=PRODUCT&DCCPO=true

 

[bluerm166]

I've just cut a new rudder stock from 9.5 aluminium plate (6082 T6) and successsfully tapped it to fit 6mm studs,with the tapping not passing all the way through the precisely matched drilling.The studs were left with the hex heads on for future tightening of the stud and separate locknuts hold the fixed item (small anodes) against the plate.Having put a convincing force on test studs I was happy that the thread wouldn't pull out for the duty involved.The OP has a different grade but I suspect that the pull out would be more than enough on M8 bolts at these centres to compress the gasket evenly.But since it's the perimeter seal that counts an access could be made in the backplate and nuts/bolts employed.Or I can provide a piece of 9.5mm plate if the OP wants to establish the torques achievable.