[N_Cook]

I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract. Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

[anorton]

"N_Cook" wrote in message
...
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points. There
are 8 off , 1mm tapped holes with 5 threads per hole , in the aluminium
available (used for undemanding normal fixing to the chassis) , if I drill
a plate to take 8 screws . The only screws of that thread I have are brass,
probably preferable to steel anyway. For a similar hub-pulling where there
was purchase , after heating (limited as to amount that can be used ),
required about 4Kg of force to extract. Would 4Kg , assuming even
distributed loading over the 8 screws be above or below the stripping force
?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

I would be leery of using these screws for even this kind of light pulling.
Even if a single 1 mm screw in a 1.25mm deep hole in aluminum can hold 0.5
kg (I do not know; I have not done the calculation), I know from experience
it is very easy to strip an M1X0.25 screw in aluminum even when torquing for
preloading. Don't forget the preload and load together have to be less than
the strength of the thread. If you do not have any preload (i.e. the screws
are loose) then there is a good chance the force will not be evenly
distributed among the screws when you pull.

I think I would try to use a method that used some sort of temporary tape or
adhesive that is compatible with the moderately high temperature you need.
If there is a large enough flat area to mount to, perhaps just viscous high
temp grease between the hub and the pulling plate would provide enough
suction force when pulled straight up.

[dpb]

On 9/7/2013 10:39 AM, N_Cook wrote:
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract. Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

The _rough_ back-of-envelope estimate here comes out at only about 20
lbf loading each assuming a soft Al. T6061 w/ a hard fastener might be
closer to 100 lbf.

--

[Ned Simmons]

On Sat, 07 Sep 2013 12:41:00 -0500, dpb wrote:

On 9/7/2013 10:39 AM, N_Cook wrote:
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract. Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

The _rough_ back-of-envelope estimate here comes out at only about 20
lbf loading each assuming a soft Al. T6061 w/ a hard fastener might be
closer to 100 lbf.

I get 30 pounds, but maybe your aluminum is softer. And I didn't have
the benefit of a napkin. g

In any case, if the screws are not silicon bronze or some other high
strength alloy, it's probably a toss-up between stripping the threads
and breaking the screws.

--
Ned Simmons

[anorton]

"Ned Simmons" wrote in message
...
On Sat, 07 Sep 2013 12:41:00 -0500, dpb wrote:

On 9/7/2013 10:39 AM, N_Cook wrote:
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract. Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

The _rough_ back-of-envelope estimate here comes out at only about 20
lbf loading each assuming a soft Al. T6061 w/ a hard fastener might be
closer to 100 lbf.

I get 30 pounds, but maybe your aluminum is softer. And I didn't have
the benefit of a napkin. g

In any case, if the screws are not silicon bronze or some other high
strength alloy, it's probably a toss-up between stripping the threads
and breaking the screws.

--
Ned Simmons

In practice I think both your estimates are overly optimistic. In this tiny,
fine thread, the clearance is usually a large fraction of the total thread
depth, so the threads just engage near the tips. Usually the failure mode is
that the tips round over instead of shearing off. Optical equipment I work
with sometimes has these tiny screws.

[Bob Engelhardt]

On 9/7/2013 8:33 PM, anorton wrote:

In practice I think both your estimates are overly optimistic. In this
tiny, fine thread, the clearance is usually a large fraction of the
total thread depth, so the threads just engage near the tips. Usually
the failure mode is that the tips round over instead of shearing off.
Optical equipment I work with sometimes has these tiny screws.

Ah ... good point. Another nugget of RCM knowledge. Bob

[N_Cook]

On 08/09/2013 01:33, anorton wrote:

"Ned Simmons" wrote in message
...
On Sat, 07 Sep 2013 12:41:00 -0500, dpb wrote:

On 9/7/2013 10:39 AM, N_Cook wrote:
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that
thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract.
Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

The _rough_ back-of-envelope estimate here comes out at only about 20
lbf loading each assuming a soft Al. T6061 w/ a hard fastener might be
closer to 100 lbf.

I get 30 pounds, but maybe your aluminum is softer. And I didn't have
the benefit of a napkin. g

In any case, if the screws are not silicon bronze or some other high
strength alloy, it's probably a toss-up between stripping the threads
and breaking the screws.

--
Ned Simmons

In practice I think both your estimates are overly optimistic. In this
tiny, fine thread, the clearance is usually a large fraction of the
total thread depth, so the threads just engage near the tips. Usually
the failure mode is that the tips round over instead of shearing off.
Optical equipment I work with sometimes has these tiny screws.

Yes I would not say they were a tight fit. Decided to suck it and see
and potentially sacrifice half a tapped hole. So 3 turns only engaged in
one tapped hole and a spring balance, I took up to 2Kg with no problem.
So I'm now confident that 8x five thread screws and a compressible
washer/pad of silicone rubber under each screw head , will take the 5Kg
via an added hole-matching load-sharing plate

[Joe gwinn]

In article , N_Cook
wrote:

On 08/09/2013 01:33, anorton wrote:

"Ned Simmons" wrote in message
...
On Sat, 07 Sep 2013 12:41:00 -0500, dpb wrote:

On 9/7/2013 10:39 AM, N_Cook wrote:
I need to do a hub-pulling type operation on a small piece of equipment
that is not made to be taken apart, so no purpose-made anchor points.
There are 8 off , 1mm tapped holes with 5 threads per hole , in the
aluminium available (used for undemanding normal fixing to the chassis)
, if I drill a plate to take 8 screws . The only screws of that
thread I
have are brass, probably preferable to steel anyway. For a similar
hub-pulling where there was purchase , after heating (limited as to
amount that can be used ), required about 4Kg of force to extract.
Would
4Kg , assuming even distributed loading over the 8 screws be above or
below the stripping force ?
I found these sites but not applicable for my purpose it would seem

www.tribology-abc.com/calculators/e3_6e.htm
http://www.roymech.co.uk/Useful_Tabl...ead_Calcs.html

The _rough_ back-of-envelope estimate here comes out at only about 20
lbf loading each assuming a soft Al. T6061 w/ a hard fastener might be
closer to 100 lbf.

I get 30 pounds, but maybe your aluminum is softer. And I didn't have
the benefit of a napkin. g

In any case, if the screws are not silicon bronze or some other high
strength alloy, it's probably a toss-up between stripping the threads
and breaking the screws.

--
Ned Simmons

In practice I think both your estimates are overly optimistic. In this
tiny, fine thread, the clearance is usually a large fraction of the
total thread depth, so the threads just engage near the tips. Usually
the failure mode is that the tips round over instead of shearing off.
Optical equipment I work with sometimes has these tiny screws.

Yes I would not say they were a tight fit. Decided to suck it and see
and potentially sacrifice half a tapped hole. So 3 turns only engaged in
one tapped hole and a spring balance, I took up to 2Kg with no problem.
So I'm now confident that 8x five thread screws and a compressible
washer/pad of silicone rubber under each screw head , will take the 5Kg
via an added hole-matching load-sharing plate.

I'd use belleville spring washers under each screw head, not rubber.
Alternately, a big washer to spread the load onto the rubber.

http://www.mcmaster.com/#belleville-disc-springs/=ofahsv

http://en.wikipedia.org/wiki/Belleville_washer

Joe Gwinn

[dpb]

On 9/8/2013 2:47 AM, N_Cook wrote:
....

Yes I would not say they were a tight fit. Decided to suck it and see
and potentially sacrifice half a tapped hole. So 3 turns only engaged in
one tapped hole and a spring balance, I took up to 2Kg with no problem.
So I'm now confident that 8x five thread screws and a compressible
washer/pad of silicone rubber under each screw head , will take the 5Kg
via an added hole-matching load-sharing plate

That seems incredible to me from the initial description...

--

[N_Cook]

Came apart without problem, Al plate with matching holes, silcone pads
and small thin wahers under the screw heads. Frame fitted to the plate
and a pair of circlip pliers in the gap to push abainst the spindle