A little jiggy-jiggy

[AdeV]

It's new project time! 

There's no point in doing small simple stuff, so to get my CNC juices flowing, it's time to build a sump-mk2-holding jig for the machine.

There's a few ground rules:

 - The machine envelope is not big enough to cut a BMW sump in one go, so it must be possible to reverse the sump on the plate. That does have one benefit, I can do all of my clamping outside of the machining area, so there's a reduced risk of smashing cutters on clamps.
 - The jig must be removable, and replacable, with minimum effort
 - The jig must be suitable for a MadModder Projectitus [shouldn't that be Projectitis? -ed] build log 
 - No actual jiggy-jiggy will be performed.

So... the first job is to scour the workshop for some suitable items:



I found the metal plate about 3 miles away at Mersey Metals  34 quid!! For a piece of 1/4" steel a mere 1ft by 1metre! Maybe it was the mixed measurements that put the price up... The big wax lump may look hauntingly familiar. You can probably guess where this is going...

The bit you didn't spot is the elderly worn out boring bar....



On the prowl for some blocks which would be a nice tight fit in the table slots, this old boring bar came up trumps. As it's truly worn to a nubbin, I am going to re-purpose it guilt free (even though it is high-quality tool steel....


So... here's the plan (apologies it's a little large, if I shrink it the text is unreadable):



First operations (on a slightly oversized piece of aluminium) will be to drill all of the mounting holes that can be reached. Some short dowels will then be screwed into holes on the jig plate, the sump is then turned around and put back on the plate, the dowels should drop nicely into the new holes providing an accurate position of the piece on the jig; the remaining holes are then drilled.

After that.... I haven't decided yet...

The clamp will probably be in the form of a strap going across the top, held down with 2 flange nuts, onto 2 posts which will be attached to the tabs on the plate. It will mainly be there to ensure the dowels aren't taking any significant lateral machining forces; but since I anticpate putting at least 4 & probably 6 or even 8 dowels in, I'm hoping it'll all hang together nicely.

Any thoughts? Am I on the right track or have I missed something dead obvious?

[Rob.Wilson]

And here is me thinking we were going to see you doing a JIG    Ade ,,, disappointed   


thats a canny lump of machinable wax you have there 


Rob

[AdeV]

The day you see me dancing, Rob, will be the day they crack open the box of novelty pullovers and skating boots "down there"... (no, not in Sydney). I will let my banana do the dancing: 

Anyway, today we were visited from on high. And verily, did the boss take up valuable workshop time, but he does pay us mere underlings, and therefore without him, lo! - neither the workshop nor all the fine toys within would have come to pass, amen....  So, having shaken the boss off, it was down t'workshop for more jiggling. Then straight back to the office to pick up the set of collets I'd forgotten to bring with...

Anyway, today I hacked off a 410mm lump of the steel. Clamped it down & drilled 6 off 1/2" holes (for the T-nuts - I've gone for 6 because the plate isn't quite flat, and it needs to be). It vibrated quite a lot & splashed coolant all over me, looks like I'll be learning speeds & feeds again... thank goodness for the feed rate override, is all my 1/2" cutter can say...



And now the job stalls for a day.... unbelievably, considering the number of endmills I've bought over the years, I haven't got a single 60 degree chamfer cutter, which I need because the T-nut screws have to go in flush. I don't want to cut 90 degrees, as that will reduce the amount of metal for the screw to hold onto....

So, time to hit the tool shops. It's a hard life... 

[AdeV]

"I haven't got a single 60 degree chamfer cutter, which I need because the T-nut screws have to go in flush. I don't want to cut 90 degrees, as that will reduce the amount of metal for the screw to hold onto...."

Then again, 90 degrees seems to be pretty standard.... so I've done that instead. Just need some countersunk 1/2" UNC screws now, I've found one place on t'net that does them, I'll have a chat with my local screw emporium (yes, I have one of those...) as well 

[AdeV]

Made a little more progress today.... my local screw emporium came up with the minerals - 6 off 1/2" UNC countersunk stainless steel machine screws 1 1/4" long. For a fiver. Well, who was I to argue?

I had to cut around 1/4" off each screw, at full length they'd bottom out on the table & that wouldn't do at all. So, today I further countersunk the holes (they weren't deep enough), managed to crash the countersink toolbit into the table while in full rapid traverse - fortunately it's a very sturdy toolbit & survived without damage. The machine also took it in its stride, it needed a re-boot though...

So... with the screws shortened, t-nuts filed to fit the slots, I faced the plate up so it's all nice and true:



Finally:



What I'm already loving about this machine - even though I did the chamfering "manually", I used a short program to go to each hole - waaay faster than a manual machine.

Next jobs - profile the edges to their final dimensions; drill the holes for the locating nubbin things, make the nubbins...

[Brass_Machine]

Hi Ade!

You got a good start going.

You are going to use the old boring bar to line the fixture up on the table?

Eric

[Brass_Machine]

It's new project time! 

 - The jig must be suitable for a MadModder Projectitus [shouldn't that be Projectitis? -ed] build log 
 

Fixed 

[AdeV]

Hi Eric,

Yep - the plan is to chop the boring bar up into segments, these will be bolted to the bottom of the plate and will fit into the slots on the machine. By having 2 on the Y-axis & 2 on the X-axis, it should be impossible to put the plate in the wrong place; and it should be repeatable to within a couple of thou, which will save me loads of time when putting a sump on or off the machine. When I was making the original, I must have spent a good couple of hours (overall) lining the thing up and edge-finding for the DRO - this jig should save all of that hassle.

[AdeV]

So, a few days have passed... I turned the plate over on the mill, and clamped it up on some parallels, so I can now cut the outline shape of the plate out. At this point, a problem reared its head; the t-nut bolts are awfully close to the edge.... Rather than make the whole thing wider, I decided to make life hard for myself & cut an arc-shaped bit into the profile, so it widens out near the bolts.

Cue lots of  and more than one  ... I'd programmed everything up OK (I thought), but the machine moaned about a circle error... Eventually I discovered that MS Visio (which I've been using as a sort of CAD-lite) had mis-measured the arc, rounding up to the nearest millimetre. After a bit of  , some more  , eventually I got the bugger to work...

First try: And another fine use for a Sharpie pen....



So, the next trick was to re-center the coordinates so the line was in the right place, then draw it again:



And, finally, as I wanted it to mill outside the shape, I turned on the radius compensation.... and it NEARLY got it right; I can't quite mill the plate full width where the tabs are, not enough space; so I come to a stop, lift the cutter, move the tab width across, down & carry on; but the radius compensation was trying to move the Y axis out of bounds.... After a lot more  , a bit of  some more  I finally managed to get it to go where I wanted... And here it is, doing cutting another 2mm or so:



It hasn't finished yet, another 5 mins and it will be done. Gotta love that...

[AdeV]

Hmm, OK, 10 mins then, plus cleanup time (and more  )...



Next job, while it's still accurately located, is to mill slots for the guide pieces to fit in, and drill the holes for the dowel pins.

[Brass_Machine]

Hi Eric,

Yep - the plan is to chop the boring bar up into segments, these will be bolted to the bottom of the plate and will fit into the slots on the machine. By having 2 on the Y-axis & 2 on the X-axis, it should be impossible to put the plate in the wrong place; and it should be repeatable to within a couple of thou, which will save me loads of time when putting a sump on or off the machine. When I was making the original, I must have spent a good couple of hours (overall) lining the thing up and edge-finding for the DRO - this jig should save all of that hassle.

That's a great idea... I have used something similar on a few jigs. Not sure if it will apply here, but one thing I found was to attach the locating pins/blocks to the jig before doing machining on the jig. This was a way to ensure that it would be square from the start.

[Brass_Machine]

...
Next job, while it's still accurately located, is to mill slots for the guide pieces to fit in, and drill the holes for the dowel pins.

Derp! And there it is... ignore my previous post.

[AdeV]

Hi Eric - yep, you got it  The underside of the jig is where all the accuracy happens, so it's staying bolted down now until the last drilling operation; which will happen soon (Sunday, I hope).

Meanwhile, today, I did yet more hard sums      - and finally cut a 1mm deep set of guide slots for the positioning blocks, thusly:



Handily enough, they fit nicely, needing a gentle tap with the hammer to sit fully home. So tonight's final operation was to drill the mounting holes (5mm mill for 6mm tap); tweak the program, run, job done:



So, the final drillings will be the dowel pin holes, I'll do all the tapping on the manual mill with the tapping head, I'm not confident enough to tap on the CNC machine yet...

Anyway, that'll all have to wait 'cos it's late and I've got a long day tomorrow... there's a race to be had (not me driving this weekend, so I'm the pit crew), that's tomorow & Saturday out of the picture, next machining will be Sunday.