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Thread: Wickman OPG Optical Grinder.
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16th April 2014, 10:27 PM #136
Bugger,
I was hoping to send you down my optometrists script and have some glasses done.
Grahame
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25th May 2014, 10:49 PM #137GOLD MEMBER
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Can't make the lens yet Grahame, But I can grind them to fit the frame lol
Well its time to get back to work on this. I have a job lined up for it.....a form tool for the domed head of a bolt lol.
So its time to start scraping the slide.
The only alignment I think is important is that the spindle is square to the movement of the slide so that the wheel moves parallel to the movement. I think if I make a dummy spindle that can clamp a parallel in the end. Set it up so the parallel is parallel to the movement of the slide. Then roll the spindle 180 ...... if things are square it should still be parallel right? The same jig could be use to check if it's square in the other plane.. though I'm not sure this matters as much.
Ok now before I get to that I need to scrape the flat ways. Before the I think I need to scrap the ways to fit the casting.
The scraped casting is what the fixed ways bolt/pin to. It was blue with my little granite block....Looks pretty flat.
One way is "not so bad" the other "not so much". I measure it about 0.0007" low in the middle. So before I start on the working face I should scrape this face first right?
Then scrap the way face down roughly parallel and flat.
Scrape the dovetail of the non gib side flat,
Bolt/pin ways back onto the casting.
Scrape flat.
Scrape moving flat ways flat.(checking for square)
Scrape moving dovetail non gib side(checking for parallel)
Check the gib side fix way is good to go.
Scrape gib side moving dovetail.
Make new gib.
Sound like a plan?
Stuart
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1st June 2014, 12:46 AM #138GOLD MEMBER
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Ok so its all good then
Started on the dummy spindle today, after tweaking the tailstock to get it "better than" 0.01mm over 250mm, I figured to would be easier to measure the spindle than to measure the bore. The spindle has 0.04mm taper lol
Before I mill the slot in the end I figured it would be a good time to fix the spindle clamps. The crack isnt exactly a friendly shape.
Patting myself on the back for buying this DTI, I dont have another that would have done the job as easily(hey thats my excuse, it might not be a very good excuse but it will have to do). I'm wondering if another taped hole might be the go as the one thats there is a long way from the action?(I'll draw something up tomorrow)
Been practicing my hook scraping. Big ones aren't so hard..... little ones are tricky. As it making them about the same size and shape.
Stuart
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2nd June 2014, 12:35 AM #139GOLD MEMBER
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Well I started scraping today. Hook scraping seems to be a lot like flaking. When everything falls into place its easy... when its not its just a mess lol.
Stuart
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2nd June 2014, 09:54 AM #140.
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Why hook rather than push Stu?
Are you going to make a pair of hold down type clamps as Phil suggested earlier in this thread? Your sectional drawing suggests otherwise.
Bob.
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2nd June 2014, 12:39 PM #141GOLD MEMBER
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Hi Bob,
Hook scraping? No other reason than "that's whats there". Though given how good I am at it I think I'm going to give it away for the places that matter. Its hard to "aim" so I think I'd just make a bit of a mess of the oil grooves.
The drawing was a late night attempt to show "whats there". (not 100% sure I meant to post it last night lol) The blue line being the part that's broken from the casting.(the black line through the blue part isn't there, if that makes sense)
The replacement will look something like this(I think) but
Should I put an angle on the step like that(though much less)
Is about 4mm deep enough?
Should I drill and tap another hole closer to the where the clamping is?(there isnt a lot of area to the left of the bolt for that step, the clamps 20mm wide with a 10mm radius)
Do I over think these things sometimes? lol (there have been many other ideas)
I could go completely over the top and make one big clamp.
Stuart
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2nd June 2014, 04:30 PM #142.
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2nd June 2014, 05:52 PM #143SENIOR MEMBER
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What's with the dovetail and all that detail on the end. I had to go back and find the original pics.
https://www.woodworkforums.com/showth...92#post1714192
Just clean that cracked part up, machine a land, and go with a simple clamp. Redrilling the bolt closer to the housing, away from the fulcrum, would be good engineering practice, but you don't have enough meat, to go with those potatoes. Two holes close together, wont be a good thing.
Keep in mind, the bore is probably a pretty schmick fit on the spindle, what's the end of the split housing going to move 2 - 3 thou, between un-clamped and clamped. You all so have a lousy 6 inch wheel hanging off the end of it. If you got a 100 pounds of clamping there, across two clamps its never going to move, you just cant generate enough force off that wheel short of crashing it.
Where you have the undercut on the bottom side of the clamp, I'd relieve that further back from the bolt hole, extending the fulcrum. Bolt hole is on 10mm centres from the back, into 28mm over all. So you are at 1:2.8 force of bolt to force of clamping.
I'm guessing the bolts are 1/4 x 20, if the clearance hole is 6.6mm? A fully dry torque'd 1/4 by 20 bolt @ 4lb/ft produces 960 pounds axial clamping. You have two of them, but reduced by that 1:2.8 ratio. Its still 340 lbs each. What I'm saying is, you could nip them up by hand, and that's still plenty.
Regards Phil.
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2nd June 2014, 07:17 PM #144Philomath in training
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Agreed. Some gorilla deciding that it needed to be tighter could well have caused the problem in the first place. If you are going to make up fancy clamps, a pad at the front so it can't pull too much on the housing could be in order.
Me being the thrill seeker that I am I'd be tempted to weld it if it were Al but it would need really good prep. Another alternative may be a steel strap over the top. may not look as nice but at least it will hold and not stress the clamp anymore.
Michael
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2nd June 2014, 08:20 PM #145SENIOR MEMBER
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I wouldn't do that. He's never going to break the rest of that housing. Those silly "ears" that broke off. you can sort of imagine how they got broke, in the last 40 years.
That split housing will come down until it closes up on the spindle, any amount of extra force will only gain half a thou or so, and all in deflection. Putting a "limiting" land under the working end of the clamp only raises more metrology. It doesn't prevent "ham fisted" tightening, i:e you wont be able to tell if your bottoming out the split housing, or bottoming out the clamp. Failure mode will be the same, stripping out the thread. I'd prefer to know that what ever force I'm putting on the bolt, is actually being applied to the housing clamp.
The other thing I'd mention, if he moves the fulcrum out towards the end of the clamp, by moving that land away from the bolt. I'd end up with a 1/8" wide land. Preferably with a radius. That will wear and cut into the base material. I wouldn't have a limiting stop on the other side of that bolt. That will give you a false sense of security. The bolt could be done up to yield, but just be sitting on two pads. Both of them in the clamp.
Regards Phil.
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2nd June 2014, 08:32 PM #146GOLD MEMBER
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I wrote this before I left for dinner "Thinking about it a little more. I can just make it like Phil said in the first place..... and in the unlikely event there is an issue I can start adding things."
I'll take that as a "yes you do" lol
Spindle is about 0.002" under except the last 1" at the pulley end which is just a little over.
The dovetail was just an idea to be sure the clamp didnt move backwards.
So I'll make it like this in Aluminium
Stuart
Umm no you dont lol
Unlike others I cant sketch worth a damn and I can barely letter/number, so what you're looking at is a scan of a scale line drawing, done over and dimensioned in Paint
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2nd June 2014, 08:44 PM #147SENIOR MEMBER
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2nd June 2014, 08:46 PM #148Philomath in training
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My concern is that by machining in a small land (on the clamp) as well as thinning the clamp material, you are adding a stress raiser. You are right that putting another land under the clamp complicates things but this is Stuart we are talking about - man with a 1000 measuring "things". Short of putting in some sort of spring element (or tightening with a torque wrench), I can't think of another way of ensuring that the screws aren't accidentally over tightened.
Michael
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2nd June 2014, 09:16 PM #149SENIOR MEMBER
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I'm getting lost, last pic I looked at was Post 141. It's all 15mm thick x 28mm long. Unless we are heat treating it to glass hard and putting it to service in a hammer drill, I cant see "stress risers"
Stu may well be able to measue to a half a bee's dick. I still maintain, that if the end of the clamp has 2.8 times the force on the clamping end - same material. The end might wear quicker.
When you are setting up on a mill, do you really care is the clamps are 3-5 degrees on the piste?
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3rd June 2014, 01:04 PM #150GOLD MEMBER
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Well this is as far as I've gone.
There is 6mm left before the spindle. So I could machine deeper, but you wont be able to see most of the crack once the clamps are in place.
Been thinking about using a ball nose cutter so it has a nice radius............but I might be over thinking things again.
I'll just make clamps as is and see how much pressure is needed. Maybe I can get away with a couple of thumb screws.
Stuart