Author Topic: Grabby Gunmetal and Stupid Setups  (Read 7012 times)

Offline smfr

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Grabby Gunmetal and Stupid Setups
« on: September 13, 2012, 06:41:57 AM »
Well, this was disaster waiting to happen. All the warning signs were there, but I just ignored them and soldiered on  :disappointed:

I was trimming the yoke end of the eccentric to thickness with the side of a 4-flute endmill. I had the eccentric bolted to a 1-2-3 block, which was bolted to the table. I was conventional cutting, but approaching from an end.

Warning sign no. 1: it was 10pm and I was trying to "get this done" before I turned in.

Warning sign no. 2: At first, the yoke end was hanging out in thin air, but even light cuts were giving ominous "grabby" sounds and a very poor finish:



Warning sign no. 3: with a slightly heavier cut (20thou), then endmill grabbed the end of the part, and swung it and the 1-2-3 block around (it only had one holding bolt, because the hole spacing doesn't match the T-slots on my table). The part survived, but with some gouges on the end.

So, I clamp things tighter, add another 1-2-3 block and a G-clamp, and try again.

This time it grabbed again, and, of course, bent the yoke end into a nasty angle:





 :facepalm: There was much sighing. Attempting to persuade the part back caused cracking:



which I guess I could try to silver-solder. But I already had to mark out the end hole a little short because of lack of material (odd because I thought I was pretty close when slitting the part), and the gouges on the end won't get fully removed when it's rounded over:



So, these eccentrics may end up with steel rods. I'll see how much material there is around the strap end to attach a steel rod and yoke part.

Simon



Offline Stuart

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Re: Grabby Gunmetal and Stupid Setups
« Reply #1 on: September 13, 2012, 08:20:38 AM »
just cut the bent/cracked bit off and silver solder a new lump on

you could use a bit of brass if the engine is not going to do a lot of work  if it is use brass and press in a couple of PB bushes


of course a bit of PB would be better but don't use PB1 as its pink and if grabs like crazy evan griping drill bits



Stuart
My aim is for a accurate part with a good finish

Offline mzt

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Re: Grabby Gunmetal and Stupid Setups
« Reply #2 on: September 13, 2012, 10:35:05 AM »
If I got it correctly, You supported the wp. on the wrong side, allowing it to spring in the direction where the depth of cut would increase.
Thank You for the heads-up.

Marcello

This is a fitting job,
not a production job that can be measured in.

Offline swilliams

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Re: Grabby Gunmetal and Stupid Setups
« Reply #3 on: September 13, 2012, 10:47:55 AM »
"(it only had one holding bolt, because the hole spacing doesn't match the T-slots on my table). "

I realise this isn't your main problem here, but experience has lead forced me to my own personal little rule that one clamp is never enough.

Steve

Offline steamer

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Re: Grabby Gunmetal and Stupid Setups
« Reply #4 on: September 13, 2012, 11:08:59 AM »
Thanks for sharing that Simon....I've done that.....though it seemed a good idea at the time...it ended similarly....

Tried getting "one more thing" done by 10pm too........that didn't work for me either....... :hellno:

Hang in....I have faith...you'll get it.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline zeeprogrammer

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Re: Grabby Gunmetal and Stupid Setups
« Reply #5 on: September 13, 2012, 12:26:20 PM »
I can imagine the emotions...

trepidation (I'm not sure about this) followed by...
jolt of fear (oh my!) followed by...
disappointment (drat!) followed by...
resignation (of course that was going to happen) and then ending (hopefully) with...
optimism (well...I learned something and the next part will be better)

Most of my parts are a five step emotional process  :Lol:
Without the last step though I wouldn't be here.

Impatience is my biggest enemy.

Sorry to see what happened.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline smfr

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Re: Grabby Gunmetal and Stupid Setups
« Reply #6 on: September 13, 2012, 04:27:49 PM »
just cut the bent/cracked bit off and silver solder a new lump on

you could use a bit of brass if the engine is not going to do a lot of work  if it is use brass and press in a couple of PB bushes
of course a bit of PB would be better but don't use PB1 as its pink and if grabs like crazy evan griping drill bits

Stuart, by PB do you mean leaded bronze? Does that and gunmetal silver-solder OK? I'll certainly have to practice my silver-soldering before I do this.

Simon

Offline Stuart

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Re: Grabby Gunmetal and Stupid Setups
« Reply #7 on: September 13, 2012, 05:34:28 PM »
no

PB   Phosphor Bronze   , PB1 is a type it can grab a drill bit and go blue with heat in an instant , avoid like the plague

get some normal PB , the leaded bronze machines well but can be tricky to silver solder,  aluminium bronze is very hard to machine ( very hard wearing ) sometimes known as Naval bronze to silver solder aluminium bronze add some common table salt to the flux that will sort it ( about 20 % )


gun metal silver solders Ok as its a copper tin alloy , but any of the leaded and aluminium alloys can be tricky


IMHO silver solder a piece of brass on to your eccentric and you will be fine


just remember clean the join ( no need to go over board on that as the flux is very aggressive ) use a flux called Tenacity 5  ( its a high temp flux with a long active life when heated ) , do your soldering in subdued light never in direct sunlight  ( you cannot see the colour in sunlight )
get the joint to a dull red as quickly as you can, at this temp the flux will be like water and very aggressive touch on the SS rod and all will be fine,

note the T5 flux is OK for stainless steel with normal silver solder


this site has a load of very useful info on the subject ( I have no connection with them only a customer ) http://www.cupalloys.co.uk

the latest info surprised me no end is the bit on soft soldering aluminium using normal soft solder and a special flux

look down the left hand side for lots of good info


Stuart
My aim is for a accurate part with a good finish

Offline smfr

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Re: Grabby Gunmetal and Stupid Setups
« Reply #8 on: September 16, 2012, 06:29:01 AM »
Thanks for the soldering tips, Stuart. I gave it a try today, and ended up with this, which I think will work:



More details here: http://www.modelenginemaker.com/index.php/topic,128.msg6801.html#msg6801.

Simon

Offline Bearcar1

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Re: Grabby Gunmetal and Stupid Setups
« Reply #9 on: September 16, 2012, 12:43:39 PM »
Looks like that should work out well for you Simon, nice save.  :ThumbsUp:


BC1
Jim

Offline GWRdriver

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Re: Grabby Gunmetal and Stupid Setups
« Reply #10 on: April 06, 2013, 12:28:03 AM »
This why I dislike GM castings, and the growing trend by kit producers to substitute GM or (gasp!) aluminum for cast iron.
Cheers,
Harry

Offline b.lindsey

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Re: Grabby Gunmetal and Stupid Setups
« Reply #11 on: April 06, 2013, 01:30:21 AM »
Sorry about the problem Simon, but nice save ...and the rest of us learn something too.

Bill