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Stilldrillin:
Thanks for the reminder John! :clap:

I got 1 on it`s way to me...... :thumbup:

David D

spuddevans:
Well I've spent a bit of a frustrating afternoon. I started off ok with cutting out some 4mm brass for the eccentric straps and then milled the pieces square and to size. No problem there.

Then I set up a vice stop and positioned the mill table for centre drilling all 4 parts, and then centre drilled all 8 holes ( keeping up are we ?? ) That went ok too. Then I started by drilling the 2mm thru holes, and this too went ok until the last hole when the 2mm drill bit snapped halfway thru. "Easy" I thought, just turn over and drill thru from the other side. So I turned it over, centre drilled and then very cautiously drilled thru using the same bit that broke ( having just resharpened, well re-shaped the broken end on the grinder freehand, probably not that sharp and definately not the same profile, but it was good enough to finish a hole that was half bored, or at least that's what I thought)

I gingerly drilled thru to where the old bit was stuck, and hearing the telltale sound of drill on harder material ( hitting drill not brass ) I withdrew the drill and knocked the drillbit fragment thru with a fine punch. Then to finish the hole off I attempted to drill through with the same re-sharpened bit. Wouldnt you know it, the darned thing snapped the drill again :bang: :bang: Fortunately the hole had been drilled enough and I just had to knock out the 2nd broken bit. So I thought that must be all the problems over and done with :poke:

Then I started on drilling the blind holes that are to be tapped, and got the 2 holes in the 1st eccentric strap drilled without any problems or drama at all.

Then I think it was at this point that I must have been getting too smug with my own ingenuity in overcoming all the preceding problems, thinking that everything's just so easy and plain sailing. I was drilling the 3rd 1.6mm x 6mm deep hole ( to be tapped M2 ) when the bit snapped :doh: "not another bit!!!". After a bit of head scratching :scratch: and thinking of how I could recover the part it occured to me that I can just bore the holes in the other end and cut off the bit where the snapped off bit is when I shape the top of the strap.

I didnt have a spare 1.6mm bit, but checking my tapping drill chart I saw that 1.7mm is ok so I drilled the opposite end and then tapped the holes.

Now here's a kick in the teeth, Just after tapping the M2 holes I happened to turn over the part and you wouldnt believe it, the darned broken bit of the drill had fallen out :doh:

Not taking heed of all the signs telling me to quit while I was behind, I pressed on and made a start on boring out on of the straps. I didnt have any M2 screws that were long enough I used some M2 allthread and some M2 nuts. Not having the stepped cutter that John used, I progressively drilled out to 13mm ( my biggest "small" drill ) and then used my boring bar set to enlarge to a little over the size of the smallest eccentric.

Taking it out of the vice and seperating it I then found that the eccentric groove is every so slightly smaller than 4mm :bang: Not having a way to chuck the eccentric to slightly enlarge the groove, the only other option is to reduce the thickness of the strap a tiny bit. The strap fits the eccentric, but it is a press fit and totally impossible to rotate. I've sanded it down using some W&D on my granite plate, but it's not reduced enough.

I guess I might try flycutting it down by a tiny bit. But at this point I decided to heed all the signs and retired for the day. Sorry for no pics in this post, but when all started to go wrong I forgot about taking pics.

So, not much progress to show, but I guess I've learned from the experience.

Tim

bogstandard:
Tim,

When it gets that bad, throw your hands in the air, bow your head in shame, and give up for the rest of the day, if you don't, you should know by now, it will only get worse.

Been there and got the t-shirt, many, many times.

BTW, you can make the straps any shape you like, as long as they fit and don't hit anything when in operation. I only made them that shape because it would be the easiest (?) way for a beginner (or so I thought).

John

spuddevans:

--- Quote from: bogstandard on September 15, 2009, 01:54:29 PM ---When it gets that bad, throw your hands in the air, bow your head in shame, and give up for the rest of the day, if you don't, you should know by now, it will only get worse.

--- End quote ---

The voice of experience there. My inexperience is what drove me on this afternoon, I now know that when things go wrong like this again, take a step back and walk away ( muttering, if that's your thing ) and leave it for the day.

Well, if nothing else, at least I've learnt that lesson, and at least it didnt go all pear shaped on a big / hard-to-make part. ( that's my attempt at looking at the bright side )

Tim

NickG:
Tim, I often wish I'd taken a step back and slept on it. As you say, my inexperience usually drives me on too, hence finishing both of my last two nights work after midnight. Coming away has been a blessing in disguise to catch up on some sleep!

I would just keep rubbing the strap on some emery cloth, or even draw file it rather than try to flycut it I think.

Nick

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