I'm making a hand-held tarp grommet setting tool I can use on a
ladder, with dies that screw together. I can grind the shank end of a
drill bit into a radius form tool and hold it tilted forward but it
won't cut very deep before the shank rubs, although the resulting
shallow ellipse is likely good enough for this job, I'll find out how
well it flares, rolls and crimps the tubular rivet when the tool is
complete. If it doesn't work I know a guy who can modify this kind of
stuff until it does.

Drill shank cutters work better on round pulley grooves for wire cable
than for cuts into the flat end of the bar.

Is there some simple geometric way to grind an accurately circular
convex radius lathe bit that I may have missed? Concave radius forming
bits are easy to shape with a tapered Dremel stone marked at the
intended size. The taper provides clearance so the bit can be clamped
flat to cut a true circular arc.

A General drill bit grinding fixture might be the right sort of tool
if it could clamp the lathe bit flat and was sufficiently rigid. I
can't really justify the cost of a new punch grinding fixture and
haven't found a used one.
http://tool.wttool.com/tools/Punch%20Grinding%20Fixture

--jsw

"Jim Wilkins" wrote in message
...
I'm making a hand-held tarp grommet setting tool I can use on a ladder,
with dies that screw together. I can grind the shank end of a drill bit
into a radius form tool and hold it tilted forward but it won't cut very
deep before the shank rubs, although the resulting shallow ellipse is
likely good enough for this job, I'll find out how well it flares, rolls
and crimps the tubular rivet when the tool is complete. If it doesn't work
I know a guy who can modify this kind of stuff until it does.

Drill shank cutters work better on round pulley grooves for wire cable
than for cuts into the flat end of the bar.

Is there some simple geometric way to grind an accurately circular convex
radius lathe bit that I may have missed? Concave radius forming bits are
easy to shape with a tapered Dremel stone marked at the intended size. The
taper provides clearance so the bit can be clamped flat to cut a true
circular arc.

A General drill bit grinding fixture might be the right sort of tool if it
could clamp the lathe bit flat and was sufficiently rigid. I can't really
justify the cost of a new punch grinding fixture and haven't found a used
one.
http://tool.wttool.com/tools/Punch%20Grinding%20Fixture

--jsw

Lathe ball cutter mounted on a grinder? Past the pivot you get a convex
tool, inside the pivot you get a concave tool.

"Bob La Londe" wrote in message
...
"Jim Wilkins" wrote in message
...
I'm making a hand-held tarp grommet setting tool I can use on a
ladder, with dies that screw together. I can grind the shank end of
a drill bit into a radius form tool and hold it tilted forward but
it won't cut very deep before the shank rubs, although the
resulting shallow ellipse is likely good enough for this job, I'll
find out how well it flares, rolls and crimps the tubular rivet
when the tool is complete. If it doesn't work I know a guy who can
modify this kind of stuff until it does.

Drill shank cutters work better on round pulley grooves for wire
cable than for cuts into the flat end of the bar.

Is there some simple geometric way to grind an accurately circular
convex radius lathe bit that I may have missed? Concave radius
forming bits are easy to shape with a tapered Dremel stone marked
at the intended size. The taper provides clearance so the bit can
be clamped flat to cut a true circular arc.

A General drill bit grinding fixture might be the right sort of
tool if it could clamp the lathe bit flat and was sufficiently
rigid. I can't really justify the cost of a new punch grinding
fixture and haven't found a used one.
http://tool.wttool.com/tools/Punch%20Grinding%20Fixture

--jsw

Lathe ball cutter mounted on a grinder? Past the pivot you get a
convex tool, inside the pivot you get a concave tool.

I saw a Holdridge cutter at a school shop auction, with several other
bidders standing around it and drooling. IIRC it went for over $600.

I suppose I could make a base for a lathe compound, which wouldn't be
nearly as hard to wash clean after the grinding as the whole lathe. On
my South Bend the center of the tool post slot can travel from about
1/4" beyond the compound's center of rotation (between the 90 degree
marks) to slightly less than 1.5" back from it.

I'd have to mill a custom tool post block to position the end of the
bit anywhere near the pivot. For similar effort I could make a bit
holder for a 5C spin index and also grind angles on threading bits.

The grommet set worked on the first try so I don't need to modify the
roll crimp guide. A 1970's brass grommet rolled up perfectly, new
import ones from HD cracked and spread flat but remained tight in the
tarp after a two man tug-of-war.
--jsw

"Jim Wilkins" fired this volley in news:nlmtao$igv$1
@dont-email.me:

I saw a Holdridge cutter at a school shop auction, with several other
bidders standing around it and drooling.

It's a gorgeous tool, and does precisely (and well) what it was designed to
do... turn radii.

I owned the 9" lathe version for about 15 years; bought it for only ONE
project, and it paid for itself in one project. But, I ended up using it
almost never after that. Finally sold it for about $600 about three years
ago. But BOY, I sure did PAY more than that for it, new! urk!

Lloyd

On Thu, 07 Jul 2016 20:50:25 -0400, Jim Wilkins wrote:


The grommet set worked on the first try so I don't need to modify the
roll crimp guide. A 1970's brass grommet rolled up perfectly, new import
ones from HD cracked and spread flat but remained tight in the tarp
after a two man tug-of-war.


Are the import ones brass? If so anneal them and see how they fold.

"Unk" wrote in message
...
On Thu, 07 Jul 2016 20:50:25 -0400, Jim Wilkins wrote:


The grommet set worked on the first try so I don't need to modify
the
roll crimp guide. A 1970's brass grommet rolled up perfectly, new
import
ones from HD cracked and spread flat but remained tight in the tarp
after a two man tug-of-war.


Are the import ones brass? If so anneal them and see how they fold.

Yep, my plan is to buy some more, place their heads in shallow water
and anneal only the tubes with a propane torch. My small stock of the
good old ones that roll up smoothly won't be wasted on outdoor tarps.

I cut the roll-up groove with a round 5/32" HSS boring bar bit blank.
The squared-off drill bit shank which isn't as hard as the fluted end
stayed sharp long enough to cut the washer side recess in the W1 tool
steel blank but I had to carve the deeper rivet side with the 5/32"
bit. I tried to copy the cast iron punch and die that came in the old
kit.

Drill bit ends held up well enough to cut aluminum pulley grooves to
fit the rope and cable. Had they been a common fractional size I could
have milled the semicircular groove with the side of an end mill. I
used a half-round convex lathe bit hand-ground to visually match the
right sized hole in a drill bit gauge to groove a steel spring winding
mandrel. The resulting groove looks round but I wouldn't trust it as a
ball bearing race.

--jsw

On Fri, 8 Jul 2016 09:29:58 +0000 (UTC), Unk wrote:

On Thu, 07 Jul 2016 20:50:25 -0400, Jim Wilkins wrote:


The grommet set worked on the first try so I don't need to modify the
roll crimp guide. A 1970's brass grommet rolled up perfectly, new import
ones from HD cracked and spread flat but remained tight in the tarp
after a two man tug-of-war.


Are the import ones brass? If so anneal them and see how they fold.

A whole lot of the imports are brass-plated FEmutt.
My lovely set from HFT is such, but they work fair to middlin'.


--
"Government is not reason; it is not eloquent; it is force.
Like fire, it is a dangerous servant and a fearful master."
--George Washington

"Unk" wrote in message
...
On Thu, 07 Jul 2016 20:50:25 -0400, Jim Wilkins wrote:


The grommet set worked on the first try so I don't need to modify
the
roll crimp guide. A 1970's brass grommet rolled up perfectly, new
import
ones from HD cracked and spread flat but remained tight in the tarp
after a two man tug-of-war.


Are the import ones brass? If so anneal them and see how they fold.

Annealing the tube helps a lot.

Jim Wilkins wrote:

I saw a Holdridge cutter at a school shop
auction

Schools hold auctions? That's good to know, I never knew that. I hear that many schools have 3-D printers, now.

wrote in message
...
Jim Wilkins wrote:

I saw a Holdridge cutter at a school shop
auction

Schools hold auctions? That's good to know, I never knew that. I
hear that many schools have 3-D printers, now.

It was a going-out-of-business sale, since manual skills are
irrelevant in our brave new post-industrial society.
--jsw

On Fri, 8 Jul 2016 15:08:59 -0400, "Jim Wilkins"
wrote:

wrote in message
...
Jim Wilkins wrote:

I saw a Holdridge cutter at a school shop
auction

Schools hold auctions? That's good to know, I never knew that. I
hear that many schools have 3-D printers, now.

It was a going-out-of-business sale, since manual skills are
irrelevant in our brave new post-industrial society.
--jsw

A school nearby did that around 25 years ago. They auctioned off three
9" SBs that looked like they had been used as horseshoeing anvils.

--
Ed Huntress

On Fri, 8 Jul 2016 15:08:59 -0400, "Jim Wilkins"
wrote:

wrote in message
...
Jim Wilkins wrote:

I saw a Holdridge cutter at a school shop
auction

Schools hold auctions? That's good to know, I never knew that. I
hear that many schools have 3-D printers, now.

It was a going-out-of-business sale, since manual skills are
irrelevant in our brave new post-industrial society.

After we're all gone, they'll realize just how badly they need us;
when it's too late.

--
"Government is not reason; it is not eloquent; it is force.
Like fire, it is a dangerous servant and a fearful master."
--George Washington

On Fri, 8 Jul 2016 10:40:38 -0700 (PDT), wrote:

Jim Wilkins wrote:

I saw a Holdridge cutter at a school shop
auction

Schools hold auctions? That's good to know, I never knew that. I hear that many schools have 3-D printers, now.


Blink....blink...most..most...most schools hold auctions, or have an
outside company come in and hold auctions.

http://www.tlcauctions.com/


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