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Thread: The Gack... is back!
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4th Jan 2020, 03:49 PM #1Philomath in training
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The Gack... is back!
Back in the later half of 2018 Anorak Bob was asking about modular vices, which then morphed a bit sideways into free vices.
One that caught his eye (and mine too) was a vice belonging to a Gack shaper. (see https://metalworkforums.com/f65/t202...62#post1941462)
The gack had a sub-table and swivel base. I made up a swivel base casting but haven't machined that yet. At the moment, the free vice part is the main interest.
Gack131.jpg
I decided that it would make a good project and so made up a pattern for it. I had the castings made but they had to 'season' for a while, while I worked in Tasmania.
Once machined, that block is around 120 square and 32mm high - a nice compact unit that would fit on most small mills.
P1040740.JPG
It was on the list of things for sorting in the shed this Xmas break, so I bit the bullet and got stuck into it. One of the attractions for me for this style of vice is that the hold down holes can be spaced to suit the table the vice will fasten to; mine having a T-slot spacing of 2-1/4" of course would not be a problem as that is quite common, but other mills out there might have trouble finding a vice to fit if they did not make their own.
To machine it, the ends were faced off and then the surface that would become the base. Once that was done, the casting was to be cut in halves. To try to be nice to the bandsaw blade, I scored the cut line with an abrasive disc, reasoning that I would get rid of the abrasive sand, so not abrade the teeth. Unfortunately, there was a void in the casting, really hard, and it managed to strip the teeth off the blade. Eventually when I realised what the problem was, I got the angle grinder out again for the hard bit. The finished vice will need some filler...
P1040742.JPG P1040744.JPG
That drama behind me, I was able to continue on and finish machining the castings. The jaws were made from some 1/2" 'stuff'. While they could be hardened, I'd like to know that if I was going to run a cutter into a vice jaw, things were not going to shatter.
P1040749.JPG
Does it work? In a way yes - I discovered that I did not have any 3/8" SHCS the right size to hold it to the table*, so had to use standard hold downs.
The small bolts sticking out near the bottom are the pivots for the jaw. The castings need painting and as those pivots should never have to come out, I will probably loctite them in, flush them off and paint over the top so they can not be seen. Before I do that I want to use it in anger with the right fasteners just to see that it all works as it should.
P1040755.JPG
Mainly for the experience, I'm eventually hoping to sell the design and pattern to Hemingway kits in the UK.
Michael
*All the hold downs in my shed are standardised on 3/8" UNC. While the mill is metric, the interfacing hardware is not.
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4th Jan 2020, 09:00 PM #2
Hi Michael,
Bit of a bugger about those voids ! Will they fill with braze ?Best Regards:
Baron J.
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4th Jan 2020, 09:34 PM #3Philomath in training
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Possibly, but they are not critical for strength so I'll use some body filler I think. Most of the void machined away so there are just a couple of isolated spots left. Pity though. I probably could have taken the castings back if I'd discovered the void while the casting was 'fresh' but now I think I'm stuck with it.
Michael
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5th Jan 2020, 02:30 AM #4
Hi Michael,
I think that it would be worth going back to them with the pictures so they can see the problem. If they still have the pattern they might make you a new one, or at least say sorry.
The really hard skin is a clue that they have been chilled, rather than been cooled slowly.Best Regards:
Baron J.
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5th Jan 2020, 12:08 PM #5Member
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Bravo Michael it looks good
one question that always come up about a free vice jaw arrangement, does it bow the mill table ? would you be able to put a dial gauge on and then clamp on the vice to see if this is true or another internet fairytale ?
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5th Jan 2020, 01:59 PM #6Philomath in training
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The answer is yes it does, as does clamping with any arrangement, but it should be small enough that any distortion is elastic, and is probably around the micron level. I'll put a gauge on at some stage and report back.
Michael
(the reasoning -
Just about material in this world has some spring to it, even things like steel and concrete - that is, apply a load to them and they will deflect. When clamping something in a vice, the item being clamped will be compressed, the frame under the jaws will stretch a bit and because the line of action of the jaws is not the centre line of the base, there will be a torque applied to the jaws that tends to bow the base. In Steel or CI normally this would be unnoticable in normal circumstances. However, if you imagine each part of a vice (one at a time) made of rubber or some other soft material you will get the idea.
In the case of a free vice, the frame is the mill bed, so clamping in the jaws will effectively apply a torque to the bed. If you think about how thick that physically is though*, there is a lot of section thickness there to resist the torque. I would say that the frame of your mill vice is less deep so if anything, likely to deflect more.
*real machines, not soggy noodle specials...)
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7th Jan 2020, 07:54 PM #7Most Valued Member
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Hi Michael,
They looking really nice. In operation, is there a set screw at one end that puts clamping force on the jaw(s) once it's bolted down using T nuts on the mill?
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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7th Jan 2020, 08:12 PM #8Philomath in training
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7th Jan 2020, 08:47 PM #9Senior Member
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I meant to comment on this when it first started.
Looking at the pic of the cavity any decent foundry should take this casting back. Its defective. Now its been machined with little evidence left it might be harder.
I expanded the pic but could not see inside. Was the surface smooth or rough? Could be entrapped gas or the feeder has chilled off resulting in shrinkage under it.
If you are getting more made take a pic of the casting with you. This will give them feedback to eliminate the problem. Ask for a discount on you next order.
Tony
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29th Jan 2020, 04:19 PM #10Philomath in training
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Not sure this proves anything or not -
I have a block of steel between the jaws and clamped to that is a piece of flat. Adjacent to the other jaw is a DI, and the tip is contacting the edge of the flat around 300mm up. As the jaw is around 30mm high, I have a 10:1 magnification of the displacement. I set to zero and then tightened the jaw up; got around 0.04mm deflection on the indictor, so 4 micron at the jaw.
P1040782.JPG P1040783.JPG
There seems to be some play in all this though - sometimes it would not reset back to zero while other times it would. While I had the vice done up tight, I wonder whether I was getting a little bit of slip between the jaw and the table.
Certainly without the 10:1, I doubt I would have seen anything that I thought was significant though.
So to confirm the earlier pronouncment, yes, there is some deflection when the vice is tightened. It does deflect the table, but is so small that I doubt it would be noticed.
Michael
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15th Feb 2020, 05:57 PM #11Philomath in training
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Just to finish off - the vice in use. I'm taking a 1mm DoC on another casting, roughly 170mm square. Did three passes and there is no step between them, so no movement.
P1040789.JPG
In the meantime, photos, a write-up and the pattern have all gone to the UK. I'll be interested to see how popular it is.
Michael
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16th Mar 2022, 06:05 PM #12.
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Two years down the track.....
Michael,
I was looking at Hemingway's selection of kits the other day and found your Gack reincarnation. Well done!! Then I started looking at two piece or free vices again and found another two piece Gack that was available as an accessory for their H20 shaper - http://www.eurospares.com/graphics/T.../GackH20p4.jpg
Screenshot 2022-03-15 175242.jpg
Certainly a simpler design to replicate with the 'benefit' of an additional jaw clamping screw. How well does your single clamping screw work?
I had been dreaming of making a more robust vice but with robustness comes the issue of potential table distortion. The Gack's downward tilting jaws and relatively small jaw clamping screws would, I imagine, reduce the risk of distortion.
I would be interested to hear your views before putting cutter to cast iron.
Bob.
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16th Mar 2022, 06:53 PM #13Philomath in training
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I'm pretty happy with it I must admit for one of those occasional use fixtures/ tools; it seems to hold firmly and does not slip. This photo is of some lathe toolholders I made. I must admit to having a strap across the ends to ensure that the parts did not spring out, but at no time during cutting did they start moving so that I thought 'It's a good thing I have that extra strap there'
C0240_Moment.jpg
I would see the advantage of this design over the design that you have pictured as having the material there to brace things up. I would think that the L shaped brackets might bend under extreme clamping, lessening the clamping force available, but that would be about it. The single clamping screw is 3/8 (chosen so it would be common with the SHCS holdig the jaw to the table), where as the pair in the picture are probably around half that, so I would expect the overall clamping force to be around the same
Michael
PS: the casting is symmetrical, so if you wanted to clamp from both ends you could. Just add the hardware.
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18th Mar 2022, 08:00 AM #14Most Valued Member
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Hi Michael,
That clamp arrangement has come together nicely.
You should be pretty chuffed with that!
And now it's part of Hemmingway kits. What an achievement!
Well done.
Edit: the photo on their website does look like it's being used on a soggy noodle!
Simon
Sent from a galaxy far far awayGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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18th Mar 2022, 06:22 PM #15Philomath in training
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