Mag transfer block too

**Michael G** · 27th December 2014, 08:48 PM

When I saw Dale's (DSEL74 – https://www.woodworkforums.com/f65/todays-auction-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 (https://www.woodworkforums.com/f65/mag-transfer-block-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 3^rd 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
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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

**Michael G** · 27th December 2014, 09:04 PM

Machining the semi-circular part was "interesting". The preferred method would have been to put it in the lathe and if I were making two I probably would have and then cut them in half. However, I wasn't. I could have attached it to a fixture and swung that but as it was several kg, it would have been highly unbalanced and I did not have any spare hammer heads around the place. Instead I set it up on the mill with my largest boring head. I have three of them but I never seem to pick projects that would mean it was more sensible to use one of the smaller units. Clamping was interesting but I used a piece of pipe to support the clamps while at slow rpm I gradually got to a circular profile. The trickiest part was getting the material lined up and staying there when clamped. I had hoped to do the whole profile in one pass, but boring head length and Z got the better of me. No problem I thought – I'll do one half and then change boring bars to do the lower part.
Photos L to R - Front shot after I'd got clean up; rear shot showing clamping method; next 2 - action shots with boring head. Note the ratty plasma cut surface - needed around 3mm of clean up
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The top half was not bad – getting past the plasma cut edges was long and I did not quite get the 100% clean up that I would have liked but I got most of the way there. The whole set up was a bit more flexible than I would have preferred so I needed about 8 spring passes to finally get a clean up.
Photo after about 6 spring passes. I noticed chatter on the steel lamina so I gave the boring tip a quick hone and it disappeared on the next pass. The blue mark is texta. When I do a spring pass and I can still see some colour I know that I 'm not removing significant material
P1020695 (Medium).JPG

I then took out the short bar and fitted up a longer bar. While setting that up I managed to knock the half machined piece from its clamped position, so lost all datums. Lots of head scratching about what do next. The plan eventually decided on was to remove one jaw from my vice (so I had a fraction more clamping length) and after cleaning up the flat side to be parallel to the cylindrical axis, use a V block to secure the section in the vice for round two. The G clamp is probably not necessary because of the low cutting forces but the stack is around 115mm high and only the bottom 30mm is clamped in the vice.
P1020696 (Medium).JPG
It's working so far. I'm roughly concentric (within 0.1mm) between the two sections and I hope tomorrow I can mount an indicator from the boring head to get better than that. (As it was there was too much overhang from the non-machined layers to get in there straight away). Provided it is close if worst comes to worst I can probably set it up well enough for a low speed skim to get the two halves back to concentric.

Michael

**RayG** · 27th December 2014, 11:13 PM

Looks good so far...

I was wondering how to go about the same job, when I saw Dale's.. I like the idea of doing it in the lathe and make two. Maybe a holesaw to cut the blanks?

Watching with interest.

Ray

**KBs PensNmore** · 27th December 2014, 11:48 PM

How would it go if the plates were laser cut?? Possibly do the bras also?? That way all the holes would be exactly the same, and no drilling

.
Kryn

**Michael G** · 28th December 2014, 07:07 AM

Originally Posted by RayG

I was wondering how to go about the same job, when I saw Dale's.. I like the idea of doing it in the lathe and make two. Maybe a holesaw to cut the blanks?

Not sure about the holesaw. It would do it certainly but how many you would go through and how long it would take would be a question (remembering too that you are taking a hole saw around 4" diameter). I am surprised how well the boring head gets things to round so it may be a stack of squares and then round up either with a saw before turning or just take time to take off the corners little by little. My bandsaw is a basic 4x6 but with a larger saw trimming corners on a stack of parts would not be difficult.
Looking at Dale's measurements the part is not a half circle but slightly less so cutting in half and cleaning up is certainly possible. If the lamina are soldered together then brass is necessary but if Loctite is used Al steps into the picture so I may have to try that next time I need a transfer block. On each end of Dale's there are two tapped holes - I am assuming for a stop or fence but I did think that using those to attach to a jig may be another way of producing the round profile (4th axis on a mill for example)

Originally Posted by KBs PensNmore

How would it go if the plates were laser cut??

It would be a trade off - being a thermal process there would still be some slag involved and a rough edge to machine through (although more precise), so clean up would be required. I would imagine to get the parts laser cut would be several hundred $100. Cutting and drilling the rectangular plates took 3 or 4 hours from memory so it's a "how much is your time worth" thing. Probably if I made up a proper metal template the plasma cutting would have been quicker and cleaner (cutting the half rounds did not take long but the clean up added to the time). The elongation of the holes was literally a stroke or two with a file (hole was 6.5mm drill, rod was 6.35mm - not much clearance). Again it is a time thing but if this was being done industrially, a drill jig with guide bushes would be used and probably get all holes just in the right spot no problems.
Incidentally I've been told that if you want accurate holes from a laser etc, you are better off getting them to pierce a pilot hole in and drilling normally as the cutting process will not always produce a clean round hole.

I am hoping you meant "cutting brass"

Michael

**KBs PensNmore** · 28th December 2014, 05:55 PM

Yes I did mean BRASS, sorry if it offended

. You can't cut bras with a laser, you need scissors

I noted the mistake, after I read your reply
Kryn

**Michael G** · 28th December 2014, 06:30 PM

Originally Posted by KBs PensNmore

Yes I did mean BRASS, sorry if it offended

. You can't cut bras with a laser, you need scissors

(Damn. There goes that research project...)

Day two started out slowly but I got there in the end. Having got the half cylinder nearly down to size, I fossicked among the indicators and bits that I had to try and get a set up. This is the best I could do and it involved bits from 4 boxes, including a gauge pin because I did not have a rod the right size.

P1020697 (Medium).JPG

Based on that, I moved sideways 0.07mm and back 0.12mm while reducing the diameter by 0.06mm - and pretty much cracked it

. There's a little bit of daylight and a witness line but I'm happy with that.
P1020698 (Medium).JPG
I then started on the base block. After squaring it up a little I then hogged out the middle to save myself some time. One part I thought might save for a future need, but it fell apart while being cut with the slitting saw. I guess those tie bolts do something after all.

P1020700 (Medium).JPG

I was going to have a go at boring this one horizontally but space was the issue again so I went vertical again. This time I could hold the outside, so the set up was not so precarious. I used a small head this time but have to do the bore in 2 parts - the top half first so I have room for the head inside the bore for the second part. The bore is around 100mm ID. I have a scribed profile on top of the block so that when I get close I can try the half cylindrical section for size. At the moment I'm around 3mm (radius) undersize on the top section and around 7 on the lower section. I did think about boring this on the lathe between centres but this is possibly quicker - tool speed is dictated by the HSS and the boring head allows faster adjustment of diameter than a bar would. With luck the bore will be finished tomorrow.

P1020701 (Medium).JPG

Michael

**simonl** · 29th December 2014, 09:25 AM

I've been watching with interest. That's coming along really nicely Michael. You must be happy with the result so far.

Simon

**Michael G** · 29th December 2014, 08:52 PM

Originally Posted by simonl

You must be happy with the result so far.

Reasonably happy, yes. A couple of awkward moments but things are progressing.

I finished the bore today and that fits nicely. I noticed on my final pass that the vertical head was a degree out of tram (I trammed it before I started, so at the moment I have no idea how it moved. The bolts were all tight still. Impact from the boring head doing interrupted cuts?). Because the Z axis drives the table, the axis of the bore is still in the right spot but instead of a circular arc it is slightly elliptical. However, the one degree means that the sides are around 20 microns closer - I can live with that.
I lightly cleaned up the semi-circular part on the linsher, mainly to get rid of the daylight in the previous photo. The smaller the air gap the better for magnetics, so probably a good thing. Trying it on the SG after the bore was complete, it works although well enough although it is not as solid as I thought it would be. I've made up the clamping pieces and need to fit them as well as engrave the angle scale before doing a final "grind to square".

Photos of a machined half bore are not all that exciting so I'll post some more when it's together. Before I do that I want to check the SG out again. The finish I get is not quite up to my expectations. I've changed the belt and remachined the drive pulley but I'm still getting a slight ripple on what should be flat smooth surfaces. It looks to be a wheel related defect as I can alter the pattern if I speed up or slow down the traverse speed slightly. I get it even though I've just dressed the wheel which makes me think I have some vibrations coming in somewhere. Even more bracing on the grinder stand?
The best photo I can find of it is this one with the chuck half skimmed - that check type pattern

P1020605 (Medium).JPG

Michael

**DSEL74** · 30th December 2014, 12:15 PM

I'm well impressed. If it is not obvious the little holders, on one end is fixed the other has a bolt to tighten and clamp.

Instead of bras, brass or Aluminium would it also be possible to use Polycarbonate or nylon sheet. maybe resin?

**Michael G** · 30th December 2014, 05:39 PM

Originally Posted by DSEL74

Instead of bras, brass or Aluminium would it also be possible to use Polycarbonate or nylon sheet. maybe resin?

The spacer material needs to be non-magnetic, able to take some physical and thermal abuse and not be affected by coolant and other things like oil that it may come in contact with. Poly carb can stress crack if in contact with some solvents (such as those in Loctite!) and nylon will absorb water. Some (most?) plastics can relax under load, so PE may be alright, may not. Depending on type, resin may be too brittle.
However, that said there are lots of things out there and probably several that could be used if holding things together with tie bolts. (masonite maybe?)

Michael

**simonl** · 30th December 2014, 06:08 PM

Hi Michael,

As usual I'm very impressed with your efforts. It's a shame that your head somehow came out of tram. I bet you'll be trying to figure that one out for a while! I assume your quote figure of 1 deg was a figure of speech, 20 micron is not that much indeed!

WRT your chuck, I got a similar pattern on my first test piece. I'm thinking it's to do with either a balance issue or a cogging effect from using the manual handwheel which has a generously worn rack & pinion. So, I also moved the table back and forth slowly by hand with the handwheel disengaged, effectively removing the gear issue and it was still evident. The wheel I'm using was the one it came with and was made in 1984. The old wheel and the fact that the arbor has some pitting from rust may be producing an imbalance and vibrations. Running the grinder without the arbor and wheel shows a noticable reduction in noise and vibration.

I'm keen to make a couple of replacement arbors (for different sized wheels) but considering I have no capacity to do internal grinding, I'm wondering if one made up on the lathe would be good enough given I'll be using the compound for the taper.

Anyway, enough jibber jabber. I'm keen to see more pics of the transfer block AND your grinder

**Michael G** · 30th December 2014, 06:28 PM

Originally Posted by simonl

Running the grinder without the arbor and wheel shows a noticable reduction in noise and vibration.

Call me mister picky, but doesn't that defeat the purpose of having a grinder?
I have noticed that when grinding the brass parts that I don't get that pattern - like you, my wheel is the first that came to hand and is probably a bit soft. Where's Bruce when you need his insights on grinding?

Originally Posted by simonl

I'm keen to make a couple of replacement arbors (for different sized wheels) but considering I have no capacity to do internal grinding, I'm wondering if one made up on the lathe would be good enough given I'll be using the compound for the taper.

Just compound will probably give you a poor finish unless you have a very steady cranking rate but if you made up a wooden plug with the right taper on it, you could probably use that to polish it up. I want to make some hubs up too. The two methods I'm considering are either

Machine the back & bore (including taper) plus the plain/ threaded portion for the wheel & nut. Part off and then turn around to do the rest of the detail in a 4 jaw.
Machine several blanks doing the rear face, taper, bore and counter bore for holding screw. Machine up an arbor that matches the spindle and without removing that from the chuck, mount all the blanks successively to machine up all the other detail. Provided that the arbor is not disturbed then everything should be concentric.

Haven't decided which way to go yet. The hub taper looks to be 1:12

Today I got side tracked onto a couple of jobs that "won't take long" so didn't get to fitting up the transfer block. It's been sitting there in the shed all day, whispering "Finish me, finish me!" Damn talking blocks.

Michael

**Michael G** · 30th December 2014, 07:41 PM

Photos of the pieces of metal that spent all day taunting me -
The bored trough. The tool twisted in the bar holder, so had extreme negative rake on it. The grind had a lot of relief on it (like a shear tool) perpendicular to travel, so that probably mitigated for the rake angle. Despite the problems, the finish came up alright.
P1020702 (Medium).JPG
The half cylinder after removing faint traces of daylight on the linisher. The black mark that can be seen is a spot that did not clean up from the plasma cutting.

P1020703 (Medium).JPG

Together. I was tempted to lap the two pieces in together until I realised that they then would fit perfectly, minus the thickness of the sandpaper/ emery. As it was the fit was darn good anyway (I linished the half cylinder before doing the final bore, not that much material was removed).
P1020705 (Medium).JPG
The clamp pieces waiting to go on.
P1020706 (Medium).JPG

The one degree was as indicated on the head. The zero mark on the head does not line up with the scale when the head is trammed (another one of those "I've got to fix that" jobs). 100mm (approximate diameter of the bore)x (1 - Cos 1 degree) = 0.015mm - not worth worrying about. It could be fixed if I straightened everything up and carefully rebored on the same centreline but for the amount of error I did not think it worth the stuffing around.

Michael

**simonl** · 30th December 2014, 08:08 PM

Theres something about the laminations of two different metals in these transfwer blocks, they look really nice to the eye. I dare say you have tried it on the mag chuck to see how it transfers with a small part on top?

WRT running the spindle without the arbor and wheel, it was purely to compare any vibrations with and without.

Good work Michael.

Simon

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