Scratching parts

[tait03]

Hello,

We're having issues getting larger parts off our surface grinder without scratching them.

We're trying our best to get all grinding compound out of any holes before removing the part and making sure the magnet has no residual mag in it when we begin to remove, but are still having issues. Does anyone have advice/suggestions to help prevent this.

thanks!

 

[eKretz]

How large are the parts? On very large stuff I always used a lifting magnet and the crane to pull them straight up. No scratching that way. If they're still easily man-liftable, try a piece of paper under the part before you start grinding. That usually helps immensely. Also if they're not too heavy, a blast from an air gun directed up close (like touching) at the corner of where the part meets the chuck will often make them come up a lot easier. Finally: ensure that you are rocking the part up on one corner rather than doing *any* sliding.

And I have to assume you are clearing any coolant and swarf off the chuck before attempting to lift, right? If not, as soon as you lift a corner of the part it will be pulling that mix underneath.

 

[tait03]

Hi

How large are the parts? On very large stuff I always used a lifting magnet and the crane to pull them straight up. No scratching that way. If they're still easily man-liftable, try a piece of paper under the part before you start grinding. That usually helps immensely. Also if they're not too heavy, a blast from an air gun directed up close (like touching) at the corner of where the part meets the chuck will often make them come up a lot easier. Finally: ensure that you are rocking the part up on one corner rather than doing *any* sliding.

And I have to assume you are clearing any coolant and swarf off the chuck before attempting to lift, right? If not, as soon as you lift a corner of the part it will be pulling that mix underneath.

Thanks for the reply. We have varying size in parts are chuck is 12.0" x 24.00". The larger ones are ones we have issues on. 1.25" x 12.00" x 20.00" and 3/4" x 10.00" x 14.00" so not to heavy to lift, but they suction to the plate good.

I had read some about the paper underneath the part. Is there a specific paper people use?

We are doing are best to clean off all coolant and swarf by rinsing them and rinsing all holes until no more swarf is coming out, but when we get them lifted slightly there is usually swarf under the part. Unsure if we can do anybetter removing it.

In regards to the magnet and crane do you run into any issues damaging the top surface of the part?

Thanks again for the reply any advice is appreciated.

 

[eKretz]

Hi

Thanks for the reply. We have varying size in parts are chuck is 12.0" x 24.00". The larger ones are ones we have issues on. 1.25" x 12.00" x 20.00" and 3/4" x 10.00" x 14.00" so not to heavy to lift, but they suction to the plate good.

I had read some about the paper underneath the part. Is there a specific paper people use?

We are doing are best to clean off all coolant and swarf by rinsing them and rinsing all holes until no more swarf is coming out, but when we get them lifted slightly there is usually swarf under the part. Unsure if we can do anybetter removing it.

In regards to the magnet and crane do you run into any issues damaging the top surface of the part?

Thanks again for the reply any advice is appreciated.

Any paper will do. It acts as a soft surface and also prevents any residual coolant and swarf from suctioning under the part when it's lifted. It also helps to reduce the suction to the chuck if grinding dry, but usually doesn't help much if grinding wet. I always used a few layers of paper under the lifting magnet on top also. Alternatively a thin brass shim. You can also use compressed air to blow away any residual coolant/swarf before lifting. Just be cautious where the air is directed and use "just enough" finger on the trigger so it isn't blowing swarf into any way surface junctions. Even with a magnet you'll want to "rock" the part and get one side up first, not lift straight up. You don't want to be applying large amounts of pull to the mag chuck or you could get garbage under that too.

 

[PegroProX440]

This has always been an issue with me as well. Pulling straight up with a magnet makes the part bounce up and then back down denting the chuck on occasions. Or I have had it to where the whole table would lift off the machine. Maybe pick up one corner with the magnet before centering it up.

The chuck companies should make a magnet with little air holes like an air-hockey table.

 

[eKretz]

Yeah, gotta rock the part up to a corner first, poor practice not to. I don't think the holes would help a whole lot, there still needs to be a lot of surface area in contact for good holding power. I have thought about doing that to a chuck myself but pressurizing the holes to give a bit of lift. That would clear any debris near the edges of the part too. However... I think the holes would plug up mighty quickly and become useless in short order.

 

[tait03]

I do try to

Yeah, gotta rock the part up to a corner first, poor practice not to. I don't think the holes would help a whole lot, there still needs to be a lot of surface area in contact for good holding power. I have thought about doing that to a chuck myself but pressurizing the holes to give a bit of lift. That would clear any debris near the edges of the part too. However... I think the holes would plug up mighty quickly and become useless in short order.

Any paper will do. It acts as a soft surface and also prevents any residual coolant and swarf from suctioning under the part when it's lifted. It also helps to reduce the suction to the chuck if grinding dry, but usually doesn't help much if grinding wet. I always used a few layers of paper under the lifting magnet on top also. Alternatively a thin brass shim. You can also use compressed air to blow away any residual coolant/swarf before lifting. Just be cautious where the air is directed and use "just enough" finger on the trigger so it isn't blowing swarf into any way surface junctions. Even with a magnet you'll want to "rock" the part and get one side up first, not lift straight up. You don't want to be applying large amounts of pull to the mag chuck or you could get garbage under that too.

And by "rock the part up" you mean try to get a corner lifted first to help break it free and lift it to the edge correct?

Thanks!

 

[CarbideBob]

The trick is no sliding at all or paper but even that sometimes leaves scars, I use newsprint but that affects accuracy if really picky.
Not sure in your case but with holes you may be able to put rods in the holes and twist the part up carefully.
Another method is to mill some slots in the chuck so that a prying tool can be used to "pop" it upwards and free.
A version of this is a pocket in the chuck part way in and apply big air blow to free it.
Vacuum chucks do not have not have much holding power but you then can pressurize them for release.

I should also comment on part loading. Once you put a under 4RMS done surface on the chuck you have to be so super careful of chuck cleaning and part positioning.
Are you 100% sure you did not scar the part in this step of the process? BTDT.

 

[eKretz]

I do try to


And by "rock the part up" you mean try to get a corner lifted first to help break it free and lift it to the edge correct?

Thanks!

Yep. Can't slide at all or you're going to get scratches, as Bob noted. There is always a bit of stray grit somewhere. Even a piece of dust from the air can scratch a fine finish.

 

[tait03]

The trick is no sliding at all or paper but even that sometimes leaves scars, I use newsprint but that affects accuracy if really picky.
Not sure in your case but with holes you may be able to put rods in the holes and twist the part up carefully.
Another method is to mill some slots in the chuck so that a prying tool can be used to "pop" it upwards and free.
A version of this is a pocket in the chuck part way in and apply big air blow to free it.
Vacuum chucks do not have not have much holding power but you then can pressurize them for release.

I should also comment on part loading. Once you put a under 4RMS done surface on the chuck you have to be so super careful of chuck cleaning and part positioning.
Are you 100% sure you did not scar the part in this step of the process? BTDT.

Yes, the part positioning can be tough as well. Thanks for that advice. I'll look into that some and the pocket in the chuck seems like a good idea.

Thanks for the advice!

 

[Luke.kerbey]

Do your parts have any holes?
I often uses screws or pins in holes round the sides and lever them off with a lever bar and a piece of aluminium to protect the Chuck.

also when I design my round die plates I try to make room for a locating flat. I then grind the opposite face to that last so I can use the flat to lever the plate off with a brass lever.

I would also advise to never lift anything from a mag Chuck without breaking the surface tension or “wringing” effect first. Without doing so puts serious strain on the grinder Bed and hydraulics. (I don’t think I’m the first to say this)

The paper trick does work but I’ve personally found it hard to keep my parallel faces pucker. It also makes a mess with the coolant so I don’t do it often if at all.


On one CNC grinder I’ve used it had an electromagnetic Chuck that demagnetised when it was turned off. I’m not sure if that’s common or not?
It made it immensely easier to pull stuff off after grinding.

 

[michiganbuck]

All good ideas, even stacking 3 or4 layers of card paper under a part. Stiff card paper like the post office cancel mail stuff is good for wet grinding. Some plastic band stock is good. Also, .030 to .100 shim stock is good. I have put block-ins at the go-direction and set non-tippy parts on 1/16" parallels for pry space. Parts are likely to slide in the go-direction if a not tippy parts, but not likely to lift with heavy grinding. A solid hand push can often tell if the holding is strong enough.
Sometimes a parallel hanging off the chuck edge can tell when the magnetism is low enough to lift the being-ground part.
Care to put under part lifts in a way that the part won't bend from mag pull-down.
I have set-under parallels that I use if I have to run a high-precision part on a questionable chuck because it is quicker to skim-grind the parallels than grinding a chuck.

 

[eKretz]

I've used the prybar against a ledge or against a bolt in a hole trick for rocking the part up before lifting also, that's a good suggestion. I usually cleaned the chuck well and just stuck a small ¼" thick piece of brass or aluminum down under the prybar. Another way if you don't have a ledge or hole is to clamp a c-clamp on the part and use it as a lever or alternatively use the prybar under it to lift up. Also on really big stuff I'd often just stick a 2x4 through the gap in the clamp and use it as a lever.

And yeah, make sure to break the surface tension before lifting with something like a crane, very important. Mag chucks generally aren't clamped down very tight and will lift easily, allowing coolant and swarf to get underneath. You'll be saying bye-bye to that nice flat fresh ground chuck surface pretty quick. Not to mention any other concerns like lifting the table.