When I saw Dale's (DSEL74 – http://www.woodworkforums.com/showthread.php?t=190600) auction purchase of a magnetic angle block, like a number of others I thought what a great score.
One of the interesting things I noticed about it though was its construction. Ray made up some magnetic blocks but soldered them together (http://www.woodworkforums.com/showthread.php?t=160111) . Dale's purchase looked like a set of lamina held together with nutted tie bolts. Of course, once I realised that I had to have a go at making one.
There are two parts to this device – a semi circular part and the trough it sits in. I started with the semi circular part and using some 3mm steel and 1/8" brass cut out a rough half circle with the plasma cutter. Steel that thick is not bad but brass is a real pain – I don't recommend plasma cutting it if you can help it. The template I used was made of wood and after the second one was turned into a smouldering wreck, I decided I needed to do something better for the trough. In the end as it is basically rectangular I cut with a bandsaw. Almost just as quick but better still no slag to clean off. Machining will take a longer but better than having brass spit at you.
Dale's original was ¼" thick lamina but I did 1/8" because that is what I had. Tie rods were ¼" brass and the two steel end plates were 6mm thick so that I could recess a nut 4mm into them. I could have straight tapped one end but was thinking about how to do the hard bit, not the easy bit. I originally decided that the nuts would be brass, but after thinking about it realised that steel would be fine as it was located in a steel lamina anyway.
Tie rod, brass nut and steel nut (longer because I tighten it with vice grips on the end then cut it off and retap for another use)
P1020678 (Medium).JPG
After cutting the lamina I drilled holes through them all individually. These could have been done as a stack but I was concerned that the drill would wander as it went through. A jig is essential for this and mine although crude was effective. For locating pins I used some of the 1/4" brass rod although strictly speaking I should have shaped them to form diamond pins. 2 holes were drilled out to 6.5mm while the 3rd was drilled to 7mm. I checked the stack when I had two holes in. Of the 60+ lamina, only 3 needed a little tickle with a round file. None of the brass ones did though, only the steel.
(L to R) 3 pins to define position; Hole located plus anti rotation; Two holes; Hole check
P1020681 (Medium).JPG P1020682 (Medium).JPG P1020684 (Medium).JPG P1020683 (Medium).JPG
The end plates had flat bottomed holes for the nuts. I have a set of stub drills that I've ground especially for counter boring holes (Primarily for SHCS use). Start with a standard drill and once the hole has sides, switch to the flat bottomed version.
P1020685 (Medium).JPG P1020677 (Medium).JPG
All the plates were then deburred/ cleaned up so that they would sandwich together with no air gap. The loctite has some gap filling ability but I was more concerned with strength. While brass was used (the traditional material), if using a loctite and tie rod construction there is no reason that Al could not be substituted. It would lessen the weight and probably be cheaper too. Something to think about for the next one.
Assembly of the blocks was easy. Nuts were pushed into the end plates and then the tie rods screwed in. Then it was just alternating brass and steel plates. As a bit of a cheat I have used Loctite bearing retainer between the layers. I figure with this and the tie rods it should stay reasonably together. Once stacked, I clamped it up with some G clamps, carefully tightened the tie bolts and let it sit for 24 hours to go off. I managed to snap two of the tie bolts while tightening but replacing them was straight forward – drill out the end in the nut and retap the nut thread. Using a long pin punch, knock out the old rod, put in a new one and be more careful next time…
(L to R) Start of a stack; about half way up; Completed stack showing bottom nut.
P1020686 (Medium).JPG P1020687 (Medium).JPG P1020680 (Medium).JPG
Michael
One of the interesting things I noticed about it though was its construction. Ray made up some magnetic blocks but soldered them together (http://www.woodworkforums.com/showthread.php?t=160111) . Dale's purchase looked like a set of lamina held together with nutted tie bolts. Of course, once I realised that I had to have a go at making one.
There are two parts to this device – a semi circular part and the trough it sits in. I started with the semi circular part and using some 3mm steel and 1/8" brass cut out a rough half circle with the plasma cutter. Steel that thick is not bad but brass is a real pain – I don't recommend plasma cutting it if you can help it. The template I used was made of wood and after the second one was turned into a smouldering wreck, I decided I needed to do something better for the trough. In the end as it is basically rectangular I cut with a bandsaw. Almost just as quick but better still no slag to clean off. Machining will take a longer but better than having brass spit at you.
Dale's original was ¼" thick lamina but I did 1/8" because that is what I had. Tie rods were ¼" brass and the two steel end plates were 6mm thick so that I could recess a nut 4mm into them. I could have straight tapped one end but was thinking about how to do the hard bit, not the easy bit. I originally decided that the nuts would be brass, but after thinking about it realised that steel would be fine as it was located in a steel lamina anyway.
Tie rod, brass nut and steel nut (longer because I tighten it with vice grips on the end then cut it off and retap for another use)
P1020678 (Medium).JPG
After cutting the lamina I drilled holes through them all individually. These could have been done as a stack but I was concerned that the drill would wander as it went through. A jig is essential for this and mine although crude was effective. For locating pins I used some of the 1/4" brass rod although strictly speaking I should have shaped them to form diamond pins. 2 holes were drilled out to 6.5mm while the 3rd was drilled to 7mm. I checked the stack when I had two holes in. Of the 60+ lamina, only 3 needed a little tickle with a round file. None of the brass ones did though, only the steel.
(L to R) 3 pins to define position; Hole located plus anti rotation; Two holes; Hole check
P1020681 (Medium).JPG P1020682 (Medium).JPG P1020684 (Medium).JPG P1020683 (Medium).JPG
The end plates had flat bottomed holes for the nuts. I have a set of stub drills that I've ground especially for counter boring holes (Primarily for SHCS use). Start with a standard drill and once the hole has sides, switch to the flat bottomed version.
P1020685 (Medium).JPG P1020677 (Medium).JPG
All the plates were then deburred/ cleaned up so that they would sandwich together with no air gap. The loctite has some gap filling ability but I was more concerned with strength. While brass was used (the traditional material), if using a loctite and tie rod construction there is no reason that Al could not be substituted. It would lessen the weight and probably be cheaper too. Something to think about for the next one.
Assembly of the blocks was easy. Nuts were pushed into the end plates and then the tie rods screwed in. Then it was just alternating brass and steel plates. As a bit of a cheat I have used Loctite bearing retainer between the layers. I figure with this and the tie rods it should stay reasonably together. Once stacked, I clamped it up with some G clamps, carefully tightened the tie bolts and let it sit for 24 hours to go off. I managed to snap two of the tie bolts while tightening but replacing them was straight forward – drill out the end in the nut and retap the nut thread. Using a long pin punch, knock out the old rod, put in a new one and be more careful next time…
(L to R) Start of a stack; about half way up; Completed stack showing bottom nut.
P1020686 (Medium).JPG P1020687 (Medium).JPG P1020680 (Medium).JPG
Michael
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