In the past I made a complicated (not that complicated) sliding bar
mount that bolted directly to my mid size lathe. On it I had an dial >indicator with a 2 inch range. It actually worked very well when I was
using it, and with the sliding bar I had 6 inches of working range (not
all at once). It was on my small lathe. The 8.5 x 18. Not the mini
lathe. I never progressed to that level of machining with the mini
lathe. The big (for me) 14x40 came with a 2 axis DRO. Its works well
enough and now I struggle to do manual machining without one. So much
so that hen I ordered a new knee mill for the shop I made sure to get
one with a DRO. I use all the time except for work stopped repetitive >operations like drilling hinge pins in a bunch of hinged molds.
Anyway, I have found a way to eliminate the primary operation I did on
the small lathe (radiusing alignment pins) and I am thinking a magnetic
back indicator might be useful. Well, for that machine and the old
turret lathe I picked up a few weeks ago. If for no other reason than
to help set the stops.
I can certainly make a magnetic back. I have a small inventory of rare
earth magnets I use for one particular type of mold I make. My concern
is this. Wouldn't a magnetic field in close proximity to the clockwork
for an extended period have the potential to magnetize the some parts of
the clockwork? I figure this has to have been answered by now given how
long dial indicators and magnets have been around. If so would simply
making an extra thick aluminum back of say an inch move the magnets far >enough away as to no longer be an issue?
On Fri, 19 Nov 2021 08:51:26 -0700, Bob La Londe <none@none.com99>
wrote:
In the past I made a complicated (not that complicated) sliding bar
mount that bolted directly to my mid size lathe. On it I had an dial
indicator with a 2 inch range. It actually worked very well when I was
using it, and with the sliding bar I had 6 inches of working range (not
all at once). It was on my small lathe. The 8.5 x 18. Not the mini
lathe. I never progressed to that level of machining with the mini
lathe. The big (for me) 14x40 came with a 2 axis DRO. Its works well
enough and now I struggle to do manual machining without one. So much
so that hen I ordered a new knee mill for the shop I made sure to get
one with a DRO. I use all the time except for work stopped repetitive
operations like drilling hinge pins in a bunch of hinged molds.
Anyway, I have found a way to eliminate the primary operation I did on
the small lathe (radiusing alignment pins) and I am thinking a magnetic
back indicator might be useful. Well, for that machine and the old
turret lathe I picked up a few weeks ago. If for no other reason than
to help set the stops.
I can certainly make a magnetic back. I have a small inventory of rare
earth magnets I use for one particular type of mold I make. My concern
is this. Wouldn't a magnetic field in close proximity to the clockwork
for an extended period have the potential to magnetize the some parts of
the clockwork? I figure this has to have been answered by now given how
long dial indicators and magnets have been around. If so would simply
making an extra thick aluminum back of say an inch move the magnets far
enough away as to no longer be an issue?
One way to evade the issue, and increase holding force, is to make a
cup of mild steel into which the rare earth magnet is installed with a resilient rubbery adhesive (so the magnet won't fracture over time).
This will focus the magnetic fields onto the open side of the cup.
Joe Gwinn
On 11/19/2021 9:51 AM, Joe Gwinn wrote:
On Fri, 19 Nov 2021 08:51:26 -0700, Bob La Londe <none@none.com99>
wrote:
In the past I made a complicated (not that complicated) sliding bar
mount that bolted directly to my mid size lathe. On it I had an dial
indicator with a 2 inch range. It actually worked very well when I was
using it, and with the sliding bar I had 6 inches of working range (not
all at once). It was on my small lathe. The 8.5 x 18. Not the mini
lathe. I never progressed to that level of machining with the mini
lathe. The big (for me) 14x40 came with a 2 axis DRO. Its works well
enough and now I struggle to do manual machining without one. So much
so that hen I ordered a new knee mill for the shop I made sure to get
one with a DRO. I use all the time except for work stopped repetitive
operations like drilling hinge pins in a bunch of hinged molds.
Anyway, I have found a way to eliminate the primary operation I did on
the small lathe (radiusing alignment pins) and I am thinking a magnetic
back indicator might be useful. Well, for that machine and the old
turret lathe I picked up a few weeks ago. If for no other reason than
to help set the stops.
I can certainly make a magnetic back. I have a small inventory of rare
earth magnets I use for one particular type of mold I make. My concern
is this. Wouldn't a magnetic field in close proximity to the clockwork
for an extended period have the potential to magnetize the some parts of >>> the clockwork? I figure this has to have been answered by now given how >>> long dial indicators and magnets have been around. If so would simply
making an extra thick aluminum back of say an inch move the magnets far
enough away as to no longer be an issue?
One way to evade the issue, and increase holding force, is to make a
cup of mild steel into which the rare earth magnet is installed with a
resilient rubbery adhesive (so the magnet won't fracture over time).
This will focus the magnetic fields onto the open side of the cup.
Joe Gwinn
That is not a bad idea. I'd need to look into how much the "iron"
reduces the effective magnetic field.
Typically when I use magnets for holding I have a light press fit and
high temp epoxy with a very slight air gap between the magnet and the
surface it is holding or holding to. Magnetic paper holders, hardware >holding, box closures etc. It does reduce the hold very slightly over a >surface to surface contact, but only a few thousandths is needed to
prevent impacts.
I'm not crazy about the rubber cup idea unless it is a very high shore
number to reduce likelihood of movement. Probably not a huge issue, but...
On Fri, 19 Nov 2021 10:38:22 -0700, Bob La Londe <none@none.com99>
wrote:
On 11/19/2021 9:51 AM, Joe Gwinn wrote:
On Fri, 19 Nov 2021 08:51:26 -0700, Bob La Londe <none@none.com99>
wrote:
In the past I made a complicated (not that complicated) sliding bar
mount that bolted directly to my mid size lathe. On it I had an dial
indicator with a 2 inch range. It actually worked very well when I was >>>> using it, and with the sliding bar I had 6 inches of working range (not >>>> all at once). It was on my small lathe. The 8.5 x 18. Not the mini
lathe. I never progressed to that level of machining with the mini
lathe. The big (for me) 14x40 came with a 2 axis DRO. Its works well >>>> enough and now I struggle to do manual machining without one. So much >>>> so that hen I ordered a new knee mill for the shop I made sure to get
one with a DRO. I use all the time except for work stopped repetitive >>>> operations like drilling hinge pins in a bunch of hinged molds.
Anyway, I have found a way to eliminate the primary operation I did on >>>> the small lathe (radiusing alignment pins) and I am thinking a magnetic >>>> back indicator might be useful. Well, for that machine and the old
turret lathe I picked up a few weeks ago. If for no other reason than >>>> to help set the stops.
I can certainly make a magnetic back. I have a small inventory of rare >>>> earth magnets I use for one particular type of mold I make. My concern >>>> is this. Wouldn't a magnetic field in close proximity to the clockwork >>>> for an extended period have the potential to magnetize the some parts of >>>> the clockwork? I figure this has to have been answered by now given how >>>> long dial indicators and magnets have been around. If so would simply
making an extra thick aluminum back of say an inch move the magnets far >>>> enough away as to no longer be an issue?
One way to evade the issue, and increase holding force, is to make a
cup of mild steel into which the rare earth magnet is installed with a
resilient rubbery adhesive (so the magnet won't fracture over time).
This will focus the magnetic fields onto the open side of the cup.
Joe Gwinn
That is not a bad idea. I'd need to look into how much the "iron"
reduces the effective magnetic field.
Typically when I use magnets for holding I have a light press fit and
high temp epoxy with a very slight air gap between the magnet and the
surface it is holding or holding to. Magnetic paper holders, hardware
holding, box closures etc. It does reduce the hold very slightly over a
surface to surface contact, but only a few thousandths is needed to
prevent impacts.
That can be done here as well.
I'm not crazy about the rubber cup idea unless it is a very high shore
number to reduce likelihood of movement. Probably not a huge issue, but...
It's not a rubber cup, it's a steel cup. It is not a press fit. There
should be a reasonably large clearance between magnet OD and cup ID,
the clearance being filled with slightly soft epoxy, needed to allow
for both the fragility of rare-earth magnets and the difference in
linear coefficients of thermal expansion.
.<https://amfmagnets.com/rare-earth-holding-magnets-round-hole.html>
.<https://www.magnetshop.com/neodymium-pot-magnets.html#1>
Joe Gwinn
"Bob La Londe" wrote in message news:snbho1$1ak1$1@gioia.aioe.org...
...
Your ideas do merit
consideration. Just pointing out the things that appear obvious to me.
-----------------
One that's obvious to me is that the magnet has to be retained in the cup >firmly enough that it doesn't pull out and stay attached to the work
surface. I think that means the steel cup bottom should be fairly thick and >quite flat and smooth inside and the potting compound should bond well to
the magnet.
I don't have a good suggestion for the compound because so many things I've >tried have failed. Actually my best results so far are from Gorilla-taping a >button magnet to the end of a same-diameter rod. It's not perfect but it >fails without breakage and is easily repaired.
"Bob La Londe"Â wrote in message news:snbho1$1ak1$1@gioia.aioe.org...
...
Your ideas do merit
consideration. Just pointing out the things that appear obvious to me.
-----------------
One that's obvious to me is that the magnet has to be retained in the
cup firmly enough that it doesn't pull out and stay attached to the work surface. I think that means the steel cup bottom should be fairly thick
and quite flat and smooth inside and the potting compound should bond
well to the magnet.
I don't have a good suggestion for the compound because so many things
I've tried have failed. Actually my best results so far are from Gorilla-taping a button magnet to the end of a same-diameter rod. It's
not perfect but it fails without breakage and is easily repaired.
On 11/20/2021 3:19 PM, Jim Wilkins wrote:
"Bob La Londe"Â wrote in message news:snbho1$1ak1$1@gioia.aioe.org...
...
Your ideas do merit
consideration. Just pointing out the things that appear obvious to me.
-----------------
One that's obvious to me is that the magnet has to be retained in the
cup firmly enough that it doesn't pull out and stay attached to the
work surface. I think that means the steel cup bottom should be fairly
thick and quite flat and smooth inside and the potting compound should
bond well to the magnet.
I don't have a good suggestion for the compound because so many things
I've tried have failed. Actually my best results so far are from
Gorilla-taping a button magnet to the end of a same-diameter rod. It's
not perfect but it fails without breakage and is easily repaired.
I've got a buddy who makes (and sells) a specialty grinding accessory
that is held in place with magnets. Like me he has found that the right press fit in aluminum works really well. Generally neither of us use an adhesive. If I were to use an adhesive I would likely abrade the
coating on the magnet and the inside of the hole, and use something like Devcon 2 ton epoxy. Alternatively if I was really concerned about
differing thermal expansion I might switch to something like Flex Coat
epoxy typically used in fishing rod building.
One thing to note is I've found polyester resin seems to stick to
aluminum better than epoxy. This is purely anecdotal. I have secured parts to be machined to a sacrificial aluminum back plate with epoxy before. I also make some aluminum molds for casting polyester resin
into a shape. I can break the bond with epoxy, but a fully cured
polyester bond is difficult to remove even with mild cleaners like
acetone, alcohol, or mineral spirits. On the aluminum polyester molds I
say in the description that the user MUST USE A MOLD RELEASE, and "If
you glue your mold shut I won't replace it."
I would note that the previous paragraph is based on anecdotal observations. I have not deliberately tried to glue aluminum together
or to something else with a polyester resin. I seem to recall original Gorilla glue is a polyester glue, but I could be mistaken. Of course
they now make a range of adhesives including their own claim to the best cyanocrylate(s). LOL.
On 11/21/2021 9:02 AM, Bob La Londe wrote:
On 11/20/2021 3:19 PM, Jim Wilkins wrote:
"Bob La Londe" wrote in message news:snbho1$1ak1$1@gioia.aioe.org...
...
Your ideas do merit
consideration. Just pointing out the things that appear obvious to me.
-----------------
One that's obvious to me is that the magnet has to be retained in the
cup firmly enough that it doesn't pull out and stay attached to the
work surface. I think that means the steel cup bottom should be fairly
thick and quite flat and smooth inside and the potting compound should
bond well to the magnet.
I don't have a good suggestion for the compound because so many things
I've tried have failed. Actually my best results so far are from
Gorilla-taping a button magnet to the end of a same-diameter rod. It's
not perfect but it fails without breakage and is easily repaired.
I've got a buddy who makes (and sells) a specialty grinding accessory
that is held in place with magnets. Like me he has found that the right
press fit in aluminum works really well. Generally neither of us use an
adhesive.
If I were to use an adhesive I would likely abrade the
coating on the magnet and the inside of the hole, and use something like
Devcon 2 ton epoxy. Alternatively if I was really concerned about
differing thermal expansion I might switch to something like Flex Coat
epoxy typically used in fishing rod building.
One thing to note is I've found polyester resin seems to stick to
aluminum better than epoxy. This is purely anecdotal. I have secured
parts to be machined to a sacrificial aluminum back plate with epoxy
before. I also make some aluminum molds for casting polyester resin
into a shape. I can break the bond with epoxy, but a fully cured
polyester bond is difficult to remove even with mild cleaners like
acetone, alcohol, or mineral spirits. On the aluminum polyester molds I
say in the description that the user MUST USE A MOLD RELEASE, and "If
you glue your mold shut I won't replace it."
I would note that the previous paragraph is based on anecdotal
observations. I have not deliberately tried to glue aluminum together
or to something else with a polyester resin. I seem to recall original
Gorilla glue is a polyester glue, but I could be mistaken. Of course
they now make a range of adhesives including their own claim to the best
cyanocrylate(s). LOL.
Yes I know I mentioned bedding in epoxy in a previous post, but that's
only when there is a problem fit.
On Sun, 21 Nov 2021 09:04:10 -0700, Bob La Londe <none@none.com99> wrote:
On 11/21/2021 9:02 AM, Bob La Londe wrote:
On 11/20/2021 3:19 PM, Jim Wilkins wrote:
"Bob La Londe"Â wrote in message news:snbho1$1ak1$1@gioia.aioe.org...I seem to recall original
Gorilla glue is a polyester glue, but I could be mistaken. Of course
they now make a range of adhesives including their own claim to the best >>> cyanocrylate(s). LOL.
Gorilla Glue is a polyurethane, if I recall. It does stay flexible,
but tends to foam badly with moisture. I'd read the data sheet.
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