Needing work completed

I've got a small quantity of parts(60) I'm needing ground. They are 1/2" wide by 27" long strips of steel, .100" thick. I'm needing a concave radius ground into one side of the strips the entire length. Is this something that can be done on a surface grinder?

Very likely, but it depends on the depth and engagement of the wheel face. How much curl can you accept from the finished parts? It's possible you'll induce some stress from the grind if it's aggressive enough.

What other methods have you considered for putting in the radius? What's the actual geometry?

Not sure of the actual radius diameter. Overall height is .100", .075" at bottom of radius. Doesn't need to be a perfect match. This is just for aesthetic reasons.

Minimum curl desired. There is also a 45 degree bevel on the opposite side of the radius. I'm going to see if I can mill this bevel on a fixture I'm making to work hold. Hopes are this won't induce too much stress, I'll know after the first.

I've already got the strips laser cut out of plate steel, very straight currently.

I'm open to any means of getting the radius I need.

Call around looking for someone with a CNC surface grinder.

That is a little over 1 1/4" radius. Not at all difficult to do on a surface grinder with a radius dressed on the wheel.

However, how much surface area is left on the back after you cut the 45 degree bevel? It may make it more difficult to hold on the chuck. Will need plenty of blocking and support under the bevel if it extends too far.

Bill

.240"x27" contact left on back side. So you lose approximately 50% of the contact area after bevel.

If needed I guess milling the bevel after the grind is still possible.

If we assume an edge to edge radius with a .025" chord height, then it's about 1.265R for the concave curve radius. You could dress a 1/2" wheel to have that curve, then grind it on a surface grinder with a long enough travel.

If you want an alternative, you could take a 1" diameter four or more flute endmill, and cant the head of a Bridgeport over by 22 degrees from vertical. The resulting concave profile cut by the end of the cutter would be damn close to your desired radius, certainly for cosmetic purposes. A little flap-wheel sanding afterwards would remove the marks left by the cutter edges.

Seeing as you're starting with sheet, you'll almost certainly get curling after removing most of one side. Grinding might make it worse, depends on your setup and cooling methods. Milling should be lower heat and stress. A bull-nose cutter would give a better finish, you'd have to adjust the head tilt to suit the functional radius of the cutter.

Oh, and the big cheese of the website hates undescriptive thread titles, next time you start a topic try to be clear about exactly what you're doing and what info you want. Check other topics here for examples.

You said "plate steel". I am assuming low-carbon sheet?

One other issue: You said strips 27" long. That's going to call for a decent size machine. At least a #3 milling machine if you go that way. Bridgeport table travels won't do the job.

The basic toolroom surface grinder sizes are 6x12" and 6x18" travels with 7" diameter wheels. The 12x30" travel with 14" wheels category is a full step (maybe two) up from the toolroom machines. If your strips are cut with accurate parallel edges, you could mount 20 or so at a time on a 12x30" mag chuck. Beyond 12x30", you get into 10+ ton monsters with more HP than medium-sized milling machines.

Definitely cut your bevels after radiusing.

In my shop, if I could figure out work holding, I'd be inclined to do this on a horizontal mill using an form cutter, then polish out milling marks (if needed) with abrasive on a shaped wooden block. Beveling would be basically the same setup, but with ganged bevel cutters.

Sounds like a big pain in the butt too me. There is no way this will come out even half way strait if grinding in the bevels IMHO Anyway to come up with a different aesthetic desing maybe. These will not be cheep to grind thats for sure.

Good luck

Yeah, it does sound annoying. Could you perhaps form the curve in, by using some roller dies on hearings with a matched concave/convex surface? Could the design be adapted to use this method?

My 9x48 Lagun has 27.5" of X-travel. My first thought was just what Milland said- kick the head over and mill it.

It would take a little kicking the ram and head around, but it could be made to fit in one pass.

jancollc, you do realize that your cutting tools have non-zero diameter, right? And as a consequence, you are going to eat up that oh-so-generous 1/2" of X travel margin before your cutter clears the workpiece.

sfriedberg said:

jancollc, you do realize that your cutting tools have non-zero diameter, right? And as a consequence, you are going to eat up that oh-so-generous 1/2" of X travel margin before your cutter clears the workpiece.

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I think the way he and I are describing it, the cutter width allowance would be pretty small. While it would take a bit of fixture fiddling, it could work with less than an extra 1/2" of travel.

Of greater issue is the old one of "Bridgeport-style" table sag or rock at extremes of travel, if real uniformity was critical. The way the OP has described it, the curve is cosmetic.

If there's a large number of these parts to me made, I'd be really tempted to make up a linear rail machine to cut or grind them. No great precision needed, or CNC control if done with limit switches and simple drives.

Milland said:

I think the way he and I are describing it, the cutter width allowance would be pretty small. While it would take a bit of fixture fiddling, it could work with less than an extra 1/2" of travel.

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Yep. The only thing that cuts is the low side of the tool,and the tool allowance is the arc that side of the tool inscribes over the width of the cut. It doesn't matter if the rest of the cutter is still over the part, it's not touching anything. As soon as the leading edge clears the part, the cut is finished.

You would have to get the spindle in the right position with the table at the very extent of the travel, so bumping the ram over to one side a little bit would be needed so that every bit of travel was available. If might need a tweak of the nod to get the rad even.

The finished cut is an elliptical radius, for obvious reasons.

It would be easier with more X, but there are a lot of bridgeport-class machines with 10x50 or even a little longer.

Are these strictly "ornamental" as in an architectural or furniture application?
Or are there specific functional dimensions and tolerances that must also apply?

Also, you mention the part is 1/2" wide and .1" thick.
Then you state that putting a "There is also a 45 degree bevel" on the back reduces the width down to less than 1/4" wide (".240"x27" contact left on back side. So you lose approximately 50% of the contact area after bevel")

It is not possible to put a .260" wide 45° bevel on a piece that is only .1" thick. The most would be .1" wide (reduction of back width). Are you beveling both edges? That would leave a flat .300" wide if both bevels go to a knife edge.

Most 42" table mills have 30" travel, but that is not how I'd do it. A surface grinder sounds the best solution, and less dressing of the wheel on a 10/12/or 14" wheel machine. As others mention, the material will curl. But it would probably curl more off the milling machine. I could grind it or plane it with the travels on my machines except that I don't currently have a 30" chuck. 1030 grinders are pretty common; but like mine, many don't actually have full length chucks mounted. I've got a 10 x 24 chuck mounted on the 32" travel grinder. On the planer, to do strips those dimensions "conveniently" i would also use a mag chuck with a stop at one end. My longest chuck for the planer is only 18".

For a vertical mill with the head tilted, the work would have to be fixtured to constrain is side-ways as well as to keep it from lifting. For a horizontal, it would still need some sideways constraint. With conventional cut, there would need to be something to hold the work down. Though with a one pass climb cut it might be possible to mill the shallow arc with only some sideways restraint. All milling options consider over length blanks and sacrificial ends to be cut off later. Or else a dedicated fixture. Or move hold-downs sequentially as the cut progresses.

smt