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Work holding a Featherweight 18" straight edge for machining

I think I am doing good. I finished machining the bottom. On the last pass with the ground insert, I loosened the clamps a bit and took another .002" off. On the surface plate, I could not get a .0015" feeler under any part of it, back, front sides. When I hinged it, I would get inconsistent results. The first time, I was surprised that it hinged about 1/3 of the way from the end, but then when I tried it again, it hinged in the middle. Third time, it hinged near the end, but then tried it again to show someone and it hinged in the center. The other "odd" thing I noticed, and perhaps it's normal at this stage, is it seemed to be "wringing" to the surface plate. You could feel it almost like suction when I go to life the SE off the granite. So I figure I did OK or I have a lot more work ahead of me. 😂

Time to set it up on the bottom and mill the prism face!

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I think I am doing good. I finished machining the bottom. On the last pass with the ground insert, I loosened the clamps a bit and took another .002" off. On the surface plate, I could not get a .0015" feeler under any part of it, back, front sides. When I hinged it, I would get inconsistent results. The first time, I was surprised that it hinged about 1/3 of the way from the end, but then when I tried it again, it hinged in the middle. Third time, it hinged near the end, but then tried it again to show someone and it hinged in the center. The other "odd" thing I noticed, and perhaps it's normal at this stage, is it seemed to be "wringing" to the surface plate. You could feel it almost like suction when I go to life the SE off the granite. So I figure I did OK or I have a lot more work ahead of me. 😂

Time to set it up on the bottom and mill the prism face!

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Everything points to really nice flatness.

Just for kicks you might make (assuming you do not have a roll of feeler gage stock in your box) three shims of aluminum can wall or aluminum foil. If you mic it, you will find each is extremely uniform in thickness. Now, put the shims all on one side, either point side or open side of the milled face, placing one near each end and one in the middle and sticking out so you can see an inch or so of each. If you are super close, all three will pull with some resistance. If not, use your feeler gage to build up [can wall thickness+.0005 or .001] and test the spot that pulled easily to see if it takes an additional .0005 or .001 to make that spot slide with a bit of resistance. That should give a decent indication of what variation you might have.

But the wringing is a very good sign. Did you lightly stone the milled face to remove any boogers? I always do. Also sliding it on the surface plate a few strokes may bring up a lot of uniformly spaced shiners if you are real close. (Yes, you may rock youself into an exaggerated sense of contact, but who wants to spoil the fun right now? :) )

Denis
 
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If you look closely, you can see the three brass domes the SE is sitting on. I checked the front edge with a gauge, and it's perfectly level with the mill bed. I'm going to start the milling operation tonight. I already have the head nodded to as close to 45 degrees as I can get it with the tools I have.

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Did you lightly stone the milled face to remove any boogers? I always do. Also sliding it on the surface plate a few strokes may bing up a lot of uniformly spaced shiners if you are real close. (Yes, you may rock youself into an exaggerated sense of contact, but who wants to spoil the fun right now? :) )
I just hit the edges with a file to remove any burs, but I did not stone the face. Once I finish machining the prism face, etc., I will take a closer look at the bottom again.
 
This is where I left off for tonight. I have the prism face 99% cleaned up. I'm probably going to take one more roughing pass of .015", that'll put me at about .115" total depth. Most of that was on the left side. I finally cleaned up the upper right corner of the prism face on my last pass.

After that, I'll take a couple skim passes with a ground insert, loosening the clamps as before.

I am really happy how this is coming out. Appreciate all the advice.

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This is where I left off for tonight. I have the prism face 99% cleaned up. I'm probably going to take one more roughing pass of .015", that'll put me at about .115" total depth. Most of that was on the left side. I finally cleaned up the upper right corner of the prism face on my last pass.

After that, I'll take a couple skim passes with a ground insert, loosening the clamps as before.

I am really happy how this is coming out. Appreciate all the advice.

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Before you take your final pass, I suggest measuring the width of the sole face both left and right. Ideally it should measure "fairly close." If you took most off on the left of the inclined face, then the right (the side that says "Str Rel" in yellow paint pen) sole distance from point to back will be greater than the left assuming the initial cut on the sole was about equal left and right. The prism will still work fine and scrape in fine that way, but it will look a little wonky as the rail will not be parallel to the point (convergence) of the sole and inclined face. And the depth of the finger relief between the top rail and inclined face will increase to the right. Again it will work fine, but you will probably wish it were more symmetric for aesthetic reasons. Looking as carefully as I can at your photos does suggest to me that the cut is a bit heavy on the left side that shows the result of my hardness testing "HB 15?" I can't quite read it.

Those castings are made pretty symmetric and it would be unusual to need to take significantly more off the left than the right. That is why I take a light cut or two at first to make sure that more or less the same amount is being removed on both ends of the faces.

The fix is to determine the difference in sole width and move the right side of the casting toward the cutting head an amount equal to the difference. Take a light cut after making the adjustment to make sure what you are seeing in the cut makes sense. (If you think you need to make,say a 60 thou correction, go ahead and move the right end toward the cutter 60 thou. But then set the cutter to take off only15 thou. If all is going as planned the cutter ought to exit the cut about 1/4 the way down the face. Now you are good to go.) And then finish the roughing.

You are doing great.

Denis
 
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Everything points to really nice flatness.

Just for kicks you might make (assuming you do not have a roll of feeler gage stock in your box) three shims of aluminum can wall or aluminum foil. If you mic it, you will find each is extremely uniform in thickness. Now, put the shims all on one side, either point side or open side of the milled face, placing one near each end and one in the middle and sticking out so you can see an inch or so of each. If you are super close, all three will pull with some resistance. If not, use your feeler gage to build up [can wall thickness+.0005 or .001] and test the spot that pulled easily to see if it takes an additional .0005 or .001 to make that spot slide with a bit of resistance. That should give a decent indication of what variation you might have.

But the wringing is a very good sign. Did you lightly stone the milled face to remove any boogers? I always do. Also sliding it on the surface plate a few strokes may bring up a lot of uniformly spaced shiners if you are real close. (Yes, you may rock youself into an exaggerated sense of contact, but who wants to spoil the fun right now? :) )

Denis
And if you haven’t got any shim stock, or cut up Coca Cola cans etc cut off some 1” wide by 6” long strips of paper and put them under the straight edge. They will do just as well, if you can’t pull any of them out you’re on a winner.

Another vote for getting a nice stone and using it often.
We used to buy stones for on site chilled iron roll re-finishing. They were perfect for rubbing tables, slideways etc. They were about 6” long by 2.5‘ wide at the bottom by 2” wide at the top, 3” tall. They fit into your hand perfectly. 200 grit or 400 grit.
Unfortunately I can’t find a supplier in 2023 and I gave all my old ones away.

Regards Tyrone.
 
Before you take your final pass, I suggest measuring the width of the sole face both left and right. Ideally it should measure "fairly close." If you took most off on the left of the inclined face, then the right (the side that says "Str Rel" in yellow paint pen) sole distance from point to back will be greater than the left assuming the initial cut on the sole was about equal left and right.

I had measured the sole after the first pass that cleaned up the edge, and IIRC, they were both the same measurement, or close to it. But I will check again. The rear sole of the SE is up agains the same 1-2-3 blocks that the back strap was against. So there may just be some extra flash on that part that I didn't notice. I may go ahead and make that adjustment anyway, just to get a symmetrical look. But, TBH, it wouldn't bother me a bit to leave it as-is. I like to be precise, but when it comes to some things, I'm just not that OCD about stuff that doesn't matter. :) But being my first SE, I might just try and go the extra mile.

Another vote for getting a nice stone and using it often.

A set of precision ground flat stones is on my wish list. There are a few guys out there that make them. I know Lance Baltzley grinds them and sells them, but at $250 a set, the budget doesn't allow that at this time. Soon, I hope, if I plan on using this SE for anything anytime.
 
Tyrone's stone sounds like it would be a real treat. I get by with a 9-dollar 1/2 X 1 X 4 aluminum oxide pocket stone. It gets loaded up with grit and oil after a while, but using a little low-viscosity solvent on it freshens it up. And a few swipes on a diamond bench stone provides a new (and also very flat) face. For my purposes, a superflat face is not important.

Denis
 
I went out and measured the sole again, using my finger to judge where the back of it is. The right side looks like it might be .025" wider than the left. I'll adjust with a shim of some sort. I have an old set of feeler gages that will make an excellent sacrificial shim.

Incidentally, you wrote "HB-151" on the left side.

If we're just talking about a simple pocket stone, I have a bunch of them, again, through acquisition of old machinists tool chests. Although I cannot find any reference to "A Bay State Product" anywhere on the googles. Maybe you can shed some light on what grit these are. The one in the photo alone feels pretty smooth so I imagine it's a finer grit? If I were to compare this to a piece of sandpaper, this feels smoother than even 200 grit, so I am not sure the "125" is comparable to the same scale.

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Bay State is (was?) a company that made all sorts of abrasives. They used to make a rubber cut of blade that was filled with abrasive, they were great for cutting thin wall stainless tube.
 
Some additional research indicates Bay State Abrasives was sold to Avco Corp in 1964 which was in turn bought by Textron in 1984. I've found some references to them, but the only catalog scan I found was for automotive abrasives (valve seat grinding, etc.)

My guess is these stones were made after the acquisition by Avco - why else would you stamp it with "A Bay State Product"?
 
So I went out on my lunch break today and checked again and decided I needed to take the full .060" off the right side. I don't have a decent collection of shim stock, so I grabbed a couple old sets of feeler gauges and put both .030" gauges between the SE and the 1-2-3 block. It ain't stupid if it works! I can't see an asymmetry anymore, which I now appreciate more than I thought. I don't think I am going to take any more roughing passes and will switch to the ground insert and just take a couple/few .005" (or less) passes.

Now the front edge will be my reference for machining the sides, back strap and the back of the SE. I will eventually take a ball end mill to the finger groove and finish that up, too.

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Tyrone's stone sounds like it would be a real treat. I get by with a 9-dollar 1/2 X 1 X 4 aluminum oxide pocket stone. It gets loaded up with grit and oil after a while, but using a little low-viscosity solvent on it freshens it up. And a few swipes on a diamond bench stone provides a new (and also very flat) face. For my purposes, a superflat face is not important.

Denis
We used paraffin ( kerosene ? ) as a lubricant. I think “ Norton “ made the honing stones, but they could have been on special order. Everybody who saw them wanted a couple of them. They were used in a special rig to alter the camber on rubber mill chilled iron rolls on site. We got them after the on site guys had used them.

I’ve been out doing the job as a helper. Imagine 100“ long rolls, 36” dia, running right in front of you at high speed with all the guards removed ! Very scary. One slip and you would be coming out the other side about 1” thick.

Regards Tyrone
 
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Sounds like more good progress!

Being a cheap SOB, if I need to mill the finger groove for one reason or another, I use a 1/2" common 4-flute end mill (I always use a diamond slip stone to ease those super-fragile pointed flute ends so they have relief and are have a sharp cutting edge but are actually little flats that will last several times as long as dead pointed flutes) and I tilt it about 30 degrees to the line of travel. It does a nice job of cutting a round (probably actually an ovoid but close 'nuf) recess. Sounds like your SE will be a thing of beauty once you finish it up.

Here are a couple drawings of the tip dressing---"exagerated for illustration purposes" done to the near tip only.
End Mil Flute Tip  Eased.jpgEnd Mill Flute Trimmed.jpg


Denis
 

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This isn't any advice for the OP since he's well on his way, but just to add comments to the pile of machining these things.

I got the shorter one, since I already have a longer prism and I thought this would be about right for lathe compounds and smaller stuff of that ilk. And hearkening back to my training in squaring up rawstock, I think I put it in the vise with the sole against the fixed jaw and machined the back side first. Then with this flat surface against the vise I did the bottom. Two sides now square. For dovetails the back side isn't functional, but a square reference is often useful. Now flipping it over I also machined the top side, thinking I could just as well scrape it parallel to the bottom and have another parallel for occasional use.

Setting up for the 45 degree face puzzled me for some time. I could have argued that I really only need the bottom surface since it's not a dovetail angle reference but just a flat that can get into a corner. I could test both dovetail surfaces just be flipping it over. Nevertheless, it seemed like that should also be a scraped reference so I finally just nested the back corner in V-blocks and cut the angle. Again, since I'm going from memory I'm not certain how I clamped it, but I think a bar in the groove let me put clamps in from the back. Also, as Tyrone so nicely recommends, having stop blocks that fit tightly in the T-slots is a wonderful help and I used them to locate the V-blocks . In theory that wouldn't matter in this case since the surface I'm machining is parallel to the table and I only needed to be sure that it wasn't canted where I might run into the clamping setup in the groove behind the cut. But it only takes a minute to insert the stops and not have to worry about checking end to end alignment later.

[edit] It looks like Mule hit the jackpot with a moldmaker's collection of stones to get in odd spaces.
 
It looks like Mule hit the jackpot with a moldmaker's collection of stones to get in odd spaces.

Based on the Gerstner these came out of, and the other tools, I am almost certain he was a tool maker. Lots of stuff in there I have no idea what to use it for, but I hang onto it, because the second I sell it or get rid of it, I find a use for it. I had no idea that these brass domes would come in handy so quick.
 
Back at it this afternoon. I finished machining the prism face and I feel pretty good about it. I started on the top.

Although somewhere along the way I made a mistake. When I measure the thickness, the right end is .0002" thicker than the left. But the center is .0014" thicker. I eased off the clamps and took a skim cut, same result. I figure maybe I had a bow in it when machining the bottom. Somehow.

The plan is to finish machining the other features, since they are not critical. I might come back and try taking a skim cut on the bottom, but my fear is I will be over-fixing it. I may just resort to scraping it out when I scrape in the bottom or the top. I'd like to have it as a parallel reference, although, in reality, probably not necessary.

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Back at it this afternoon. I finished machining the prism face and I feel pretty good about it. I started on the top.

Although somewhere along the way I made a mistake. When I measure the thickness, the right end is .0002" thicker than the left. But the center is .0014" thicker. I eased off the clamps and took a skim cut, same result. I figure maybe I had a bow in it when machining the bottom. Somehow.
The casting thickness of a face measured from the machined surface to the inside surface may very well vary that amount or more. The pattern is Baltic Birch and has been painted, sanded and repainted numerous times as it has been cast more than 150 times! Secondly, even if the pattern were made to very tight tolerance, because of the assymetry of the casting, the casting has some bowing in it. You can see that in a raw casting if you sight down the the convergence of the to main faces---it bows with the center portion "positive" compared to the ends. This is not a defect. It is the nature of soldifying cast iron.

So, if you are micing sole thickness and comparing the thickness of the center vs the ends, I would not conclude this indicates some error in machining. It probably means the inside surface of that face is humped up a bit. That matters not at all. (Maybe I misunderstood what you wrote?) And, I would add, if your left and right thicknesses are within .0002, wow! I'd think the surface irregularities of the as-cast inside surface of the faces would be on the order of a few thou within a 1" circle of area.

Denis.

Added: Maybe what you were measuring is across the top rail machined surface compared to the sole. Yes, if that varies .0014, something is not quite according to Hoyle. But that is not a "bad" error. It would be a cumulative error combining any lack of flatness of the top rail cut and the sole cut. Your mill table might easily run untruly enough to cause that cumulative error.
 
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I was referring to the distance measured between the sole and the top rail. My mill is much, much, less than new. 😉 There is plenty of wear in the table. So I suppose that would make sense. When the table is at the extreme left or extreme right, it probably sags that much, raising each end of the SE just enough to cause the error? Hmmm. Now I need a 48" SE. 😂

I wonder if it's feasible then to put a .0015" shim under the center some how to account for it? Not for this project, just for the next one. 🙂 I'm going to leave it as is. It'll have to be scraped out, if I decide to take it that far. I'm not too concerned at this point, based on your opinion that it's not "bad." But if I my assumption is correct, at least it's something I can work around when I need to.
 








 
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