Facing Cast Iron

[Jammer Six]

I'm confused about tool shapes for the lathe, specifically the shape I need to face a cast iron face plate. I've seen information that seems to conflict, so I'm asking.

I've read that one must take a light skim pass off a new faceplate to ensure allignment with the lathe, and I'm looking for the tool to do so.

[eKretz]

Use any tool you like that fits the geometry of the part. If it can reach the areas you need to reach and is sharp it should be fine. I'd run a small radius to minimize tool pressure, maybe 1/64" or in that ballpark, and make sure the corner you leave after facing clears any internal radius on the mating part. You can do that by making sure the radius of your tool is smaller than any radius on the mating part or by turning a slight undercut at the end of the face if there's a shoulder. I don't know your experience level so it's hard to make any further suggestions.

[SLK001]

First, mount the plate backwards and take a skim pass on the back. Flip it around, then do the same for the front. I would use a larger radius than above, say 1/16". Make sure your tool is sharp for a nice finish. If it can't shave a fingernail, it isn't sharp enough.

[Mcgyver]

imo, this is the best facing tool. I use the same geometry for fly cutters. Just create the rake by grinding a chip breaker in the end of some hss - the rake angle is exaggerated to show the shape, but you get the idea. Lasts forever.

[BCRider]

First, mount the plate backwards and take a skim pass on the back. Flip it around, then do the same for the front. I would use a larger radius than above, say 1/16". Make sure your tool is sharp for a nice finish. If it can't shave a fingernail, it isn't sharp enough.

I can see the idea of equalizing the sides. But on faceplates with a cast rear face with ribs and valleys that's not an option. On a solid plate with both sides turned I can see the idea being a good one.


_____________

Jammer Six, before you do that why not throw a dial gauge on the plate and see if it has any runout? Otherwise you might well be trying to fix a non-existent issue. The dial or test gauge does not lie. Check it at a few points out across the face. Use very little needle movement so the round ball on the end of the finger can ride over the slots without moving the body of the gauge.

If it does need a skim to true it up I'd say this is the right time for a keenly honed HSS tool. But a good choice if you're a carbide fan would be a flat topped insert or a brazed carbide tool with freshly diamond honed edges. Cast iron behaves to cutting much like brass. So to get a good cut which does not pull or push away the surface you want a keenly sharp edge as others mentioned. And my own preference would be pretty low top surface side and back rake angles In fact a dead neutral flat top works just fine.

A faceplate wants some friction for better holding the parts too. So my choice would be a pretty normal looking tool with a rather small nose radius and a somewhat aggressive inward feed so you end up with a smooth finish but a texture to the surface that looks a little bit like a record. The smoothness means there won't be a lot of burrs to catch fibers out of rags or paper towels but the texture will aid with getting more friction from a given clamping force. And reducing the clamping force needed means less distortion of the plate so it stays flatter and you get better accuracy all at the same time. In fact if it does end up with a bit of a rough texture it just means more grab so less clamping force needed and you just learn to use a brush to clean it instead of a rag.

[eKretz]

First, mount the plate backwards and take a skim pass on the back. Flip it around, then do the same for the front. I would use a larger radius than above, say 1/16". Make sure your tool is sharp for a nice finish. If it can't shave a fingernail, it isn't sharp enough.

It's absolutely not necessary to have a large radius to get a good finish. In fact, you can still get a very good finish with nearly a dead sharp point, even without massively dropping the feed. The trick is to set the tool such that the following edge almost acts as a wiper. Best of both worlds. Low tool pressure, good finish.

[JoeLee]

I can see the idea of equalizing the sides. But on faceplates with a cast rear face with ribs and valleys that's not an option. On a solid plate with both sides turned I can see the idea being a good one.


_____________

Jammer Six, before you do that why not throw a dial gauge on the plate and see if it has any runout? Otherwise you might well be trying to fix a non-existent issue. The dial or test gauge does not lie. Check it at a few points out across the face. Use very little needle movement so the round ball on the end of the finger can ride over the slots without moving the body of the gauge.

If it does need a skim to true it up I'd say this is the right time for a keenly honed HSS tool. But a good choice if you're a carbide fan would be a flat topped insert or a brazed carbide tool with freshly diamond honed edges. Cast iron behaves to cutting much like brass. So to get a good cut which does not pull or push away the surface you want a keenly sharp edge as others mentioned. And my own preference would be pretty low top surface side and back rake angles In fact a dead neutral flat top works just fine.

A faceplate wants some friction for better holding the parts too. So my choice would be a pretty normal looking tool with a rather small nose radius and a somewhat aggressive inward feed so you end up with a smooth finish but a texture to the surface that looks a little bit like a record. The smoothness means there won't be a lot of burrs to catch fibers out of rags or paper towels but the texture will aid with getting more friction from a given clamping force. And reducing the clamping force needed means less distortion of the plate so it stays flatter and you get better accuracy all at the same time. In fact if it does end up with a bit of a rough texture it just means more grab so less clamping force needed and you just learn to use a brush to clean it instead of a rag.

How would you mount the face plate backwards ?? If it's a direct mount like an L00 or similar you can't mount it backwards. And I don't believe I've ever seen one with out ribs or some arrangement of webbing. Besides what good would it do you to try and cut the back side ? unless it horribly uneven and mounded to the point where you can't squarely seat a nut. I have seen cheap import ones like that.

As far as facing and good carbide insert with a radius nose should work just fine.

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

[Mcgyver]

How would you mount the face plate backwards ?? If it's a direct mount like an L00 or similar you can't mount it backwards. And I don't believe I've ever seen one with out ribs or some arrangement of webbing. Besides what good would it do you to try and cut the back side ? unless it horribly uneven and mounded to the point where you can't squarely seat a nut. I have seen cheap import ones like that.

As far as facing and good carbide insert with a radius nose should work just fine.

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

agreed, I've never heard of facing the back side of a faceplate. Too what purposs? I won't say all because I've not seen everyone on the planet, but they are predominately ribbed cast iron on the backside.

[tom_d]

I'm confused about tool shapes for the lathe, specifically the shape I need to face a cast iron face plate. I've seen information that seems to conflict, so I'm asking.

I've read that one must take a light skim pass off a new faceplate to ensure allignment with the lathe, and I'm looking for the tool to do so.

As noted in Post #5, check to see what you have now. Before diving into removing material I would recommend mounting the plate several times to check for repeatability. Make sure there are no other problems lurking that need to be addressed. As for cutting cast iron, it should be cut dry, and the tool should have a zero rake angle. Other clearance angles at your discretion to suit the work.

[JoeLee]

I faced these with carbide.

You can see the ribs through the two slots in the first pic.



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

[J Tiers]

agreed, I've never heard of facing the back side of a faceplate. Too what purposs? I won't say all because I've not seen everyone on the planet, but they are predominately ribbed cast iron on the backside.

You would NEVER face the entire back.

I assume the idea is to assure that the surface ON A THREADED SPINDLE FACEPLATE which hits the "shoulder" is intended, and that in order to assure that the surface will repeatably mount the same exact way.

Obviously it would not apply at all to those "bloated plutocrats" who have L and D series mounting systems

[rickyb]

Use a vacuum or a face mask, it’s a messed, dusty endeavor. Cover the ways.

[old mart]

I took the 160mm chuck to bits to clean it, and while it was off the backplate, I checked the front face of the backplate for runout. It measured 0.0005" tir and as it was ready, I used a carbide insert intended for aluminium. These are very sharp and worked perfectly for the tiny ammount taken off. I made sure the surface was well marked by my dirty fingers first, so the freshly machined surface showed up.
I always machine chuck backplate all over, but faceplates are commonly cast with stiffening ribs which are left as cast.

[SLK001]

My face plate is a 3/4" piece of solid cast iron with a mounting boss about 1" deep, so the mounting area has about 1-3/4" of "meat" to hold the threads. It looks like a large chuck backplate. It will mount from either direction, so I suggested that the back be skimmed, just like a backplate would be, then, when mounted correctly, the registration of the face plate would be correct for that particular lathe. Once the user was assured that the registration was correct, the face could be faced to be parallel to the back. Of course the entire back doesn't need to be faced, only where the plate will meet with the shoulder of the spindle. All this only applies to a threaded spindle.

[darryl]

It might be looking for trouble to do any 'treatment' on the contact surface at the back of the faceplate, but a light sanding with a small flat and 400 grit paper would improve the contact area and knock off the high spots. That's about all I would do there. As far as truing the face, be aware you might be machining a slight inverted cone shape across the diameter of the plate. Check it with a straightedge before you do anything, and check it again after, just so you know what has happened.