Moving The Locatioin Of A Dowel Pin A Few Thou

[JoeLee]

Why not just shim the fingers when you need the crisp bends?

It doesn't work that way.

JL.............

[JoeLee]

An eccentric pin would want to rotate to the lowest position under load. I'd go with correcting the location of the apron and drilling/reaming for a larger pin.

I've thought of this also, and may go with correcting the location with an over size pin approach if the eccentric pin wants to rotate. The apron is held in place with two bolts on each side so not sure if it will move once tightened down. This depends on how snug a fit the pin is in the pivot arm and if it wants to rotate one pin couldn't rotate with out the other doing the same.

JL...............

[J Tiers]

An eccentric pin would want to rotate to the lowest position under load. I'd go with correcting the location of the apron and drilling/reaming for a larger pin.

I think that is questionable with a press fit pin, one that has only a few thou eccentricity in a 375 thou diameter pin. Especially if the load is in line with the eccentricity, as it seems to be in this case. The torque from the "lever arm" needs to be enough to turn the press fit.

I'd be more worried about making sure the pin actually went in with the correct part up.

[Doozer]

An eccentric pin would want to rotate to the lowest position under load. I'd go with correcting the location of the apron and drilling/reaming for a larger pin (10mm?).

No, no, no it wouldn't.
We are talking .010" offset here, and the mating pieces are bolted tight.
Never in a million years is that pin going to rotate.

-D

[MrWhoopee]

I'd be more worried about making sure the pin actually went in with the correct part up.

This is the other problem, particularly if the pin is a press fit. A slip fit with Loctite would stand a much better chance of success as you could use an indicator and rotate the pin into position. I still believe that an oversize pin is the best/easiest solution.

[JoeLee]

I think that is questionable with a press fit pin, one that has only a few thou eccentricity in a 375 thou diameter pin. Especially if the load is in line with the eccentricity, as it seems to be in this case. The torque from the "lever arm" needs to be enough to turn the press fit.

I'd be more worried about making sure the pin actually went in with the correct part up.

That's a good point JT. There isn't enough offset to make the pin want to rotate.

I should be able to visually align the pin before tapping it into the pivot arm. I might even be able to come up with a way to scribe the high point of eccentricity.

JL...............

[Rich Carlstedt]

Comment from left field, as I am not familiar with your brake and probably don't fully understand the setup as described.
If there is a distance between the plate and the pins, why not file the plate to make the distance match ?
Conversely, silver solder a shim for the distance ?
Rich

Edit : My comment assumes the pin is a stop ?

[larry_g]

Something in the back of my mind says that the axle pins in the green casting are eccentric and adjustable. Have you checked for this?

lg
no neat sig line

[JoeLee]

Comment from left field, as I am not familiar with your brake and probably don't fully understand the setup as described.
If there is a distance between the plate and the pins, why not file the plate to make the distance match ?
Conversely, silver solder a shim for the distance ?
Rich

Edit : My comment assumes the pin is a stop ?

Rich, I know I didn't do a great job of explaining myself here but here is a sketch I made. I can file or grind the top edge of the apron so that both sides are equal distances from the center of the pivot point. That's not an issue, but that just puts the top edge of the apron further below the center of the pivot point. and what happens is when the apron is raised to make a bend that surface moves away from the pivot point on the horizontal plane resulting in a larger radius bend vs a clean sharp bend.
On heaver ga. sheet metal it probably won't be noticeable but on thinner material it will. The edge of the apron moves away from the edge of the fingers.

If I was good with cad or solid works or what ever you guys use to make those nice animated working models I would draw something up to better explain this.

JL...................

[JoeLee]

Something in the back of my mind says that the axle pins in the green casting are eccentric and adjustable. Have you checked for this?

lg
no neat sig line

Ya know, that was the first thing I thought of when I started looking at this and taking it apart but I don't believe the adjust like your thinking. The pin is on center with the part that is fastened in the casting.

Thinking about it if it were eccentric and adjustable what would happen when you rotate it to raise the pivot point ?? it would also be bringing it in and the apron would hit the flat bar.

I think the only way and the easiest way would be to offset the dowel pins holding the apron in place, or as mentioned previously drill to the next size larger dia. pin after the apron is properly set.

I would rather not let this get that involved. Besides the eccentric pin idea is nice because if I ever have to adjust the apron in the future for what ever reason all I would have to do is grind another

pair of offset pins.

JL................

[BCRider]

If the fixed side that the work is clamped to is spot on and it is the working edge of the apron which is out of spec with one side lower than the other and if that same displacement from the center line holds when the apron is pivoted up then that's sure bad.

It would not have left the factory like that so I'm tending to think that there's some past damage or perhaps wear that is present. From the looks of the wear and damage to the faces the poor brake has seen better days. So I'm thinking that perhaps if you pull things apart a little more you'll find a "smoking gun" which needs fixing rather than fudging.

But yeah, if the edge of the apron maintains that difference in positioning from the pivot axis as measured from the center pins then it'll never give you nice consistent bends. At the very least it is something that you'd need to fudge with the finger adjustment feature.

[BCRider]

Joe, I've only worked on a couple of finger brakes and it was all lots of years ago. But I do recall that pretty well everything on them was in fact adjustable. I would not be at all surprised to learn that Rich is right and the end axles that the apron pivots on is in fact adjustable to fix the very issue you have. It's so critical that the working edge be dead on center height that it makes sense to make it an adjustable feature. I know you've worked on the darn thing until you're nearly fed up. But have another look to see if you can find a way to change those pivots. Like start by measuring out from that indicator pin to the rotational line for the apron and see if there is an offset/eccentric feature to it. If there is then it's got to be adjustable.

Re your diagram. I'm not sure what you're asking. But the added bar that stop or reduces the scuff marks must be at the same height as the edge of the apron. If it is lower then it won't even touch the sheet metal. If it's higher then you risk getting a funky wave in the metal on that side of the corner.

[Henro]

Just curious, but what are you doing with the brake that a few thousandths makes a difference?

Of course, I have never been the sharpest tool in the box...😀

[JoeLee]

If the fixed side that the work is clamped to is spot on and it is the working edge of the apron which is out of spec with one side lower than the other and if that same displacement from the center line holds when the apron is pivoted up then that's sure bad.

It would not have left the factory like that so I'm tending to think that there's some past damage or perhaps wear that is present. From the looks of the wear and damage to the faces the poor brake has seen better days. So I'm thinking that perhaps if you pull things apart a little more you'll find a "smoking gun" which needs fixing rather than fudging.

But yeah, if the edge of the apron maintains that difference in positioning from the pivot axis as measured from the center pins then it'll never give you nice consistent bends. At the very least it is something that you'd need to fudge with the finger adjustment feature.

The fixed side where the 1 1/2" x 3/4" bar is bolted down is pretty close to being on center with the pivot pin, each side is within about .004 of each other. That's close enough and probably within the factory tolerance.

I don't know why or how the apron ended up the way it is. It may have left the factory that way. The edge of the apron and the bar were nicked up pretty good but all that was probably from the fingers being removed and dropped and banged around etc. The fingers are not sprung or bent and they all line up nice and straight on the bar.

I've seen some of these brakes where people have tried to bend rod. You can see the impressions that it leaves on the edge of the fingers. look at some of these on ebay.

This on is really in pretty good shape for it's age. mfg, date for this is between 1974 and 80 I believe. Not cheaply made. the pivot arm and finger roll cam all pivot on Torrington needle bearings.




Here is a pic of the edge of the apron after I filled in all the little nicks. I only lost about .002 thou in the clean up process but that doesn't make any difference since I will be making the off set dowel pins. I may set it up on my grinder and clean it up a little more. What a couple more thou ?

JL........................

[JoeLee]

Joe, I've only worked on a couple of finger brakes and it was all lots of years ago. But I do recall that pretty well everything on them was in fact adjustable. I would not be at all surprised to learn that Rich is right and the end axles that the apron pivots on is in fact adjustable to fix the very issue you have. It's so critical that the working edge be dead on center height that it makes sense to make it an adjustable feature. I know you've worked on the darn thing until you're nearly fed up. But have another look to see if you can find a way to change those pivots. Like start by measuring out from that indicator pin to the rotational line for the apron and see if there is an offset/eccentric feature to it. If there is then it's got to be adjustable.

Re your diagram. I'm not sure what you're asking. But the added bar that stop or reduces the scuff marks must be at the same height as the edge of the apron. If it is lower then it won't even touch the sheet metal. If it's higher then you risk getting a funky wave in the metal on that side of the corner.

The only adjustments on this are for moving the fingers forward and backwards to adjust the gap for different thicknesses of sheet metal, and another adjustment for locking the fingers down on the bar, also to allow for different thicknesses of sheet metal.
No other adjustments for any thing else.

JL.................