Fitting a bowed magnetic chuck

[Mike1974]

It seems you are done, but something to consider if it comes up again is blanchard grinding. It would be quick work to "rough" in, and it is fairly easy to grind aluminum with open porous wheels on a blanchard.

 

[jwmelvin]

Today, finish grinding with coolant:

 

[jwmelvin]

I liked the 46H porous wheel for the initial roughing but it wasn’t the right wheel for finishing. I switched to a regular 46I and it seemed more consistent over the cut.

It’s not 100% cleaned up but I have no need to go farther now. I will try to measure it a bit soon (leaving it on the set pad).

Thanks for the guidance everyone especially @michiganbuck

 

[michiganbuck]

looks like a job well done.
The 46H porous wheel might become your down grinding wheel or saver for chuck grinding.
Perhaps let the guys here know where you got the wheel and its cost.

 

[jwmelvin]

looks like a job well done.
The 46H porous wheel might become your down grinding wheel or saver for chuck grinding.
Perhaps let the guys here know where you got the wheel and its cost.

The porous Norton wheel I bought from McMaster for $45, after buying a CGW porous wheel on eBay where the seller sent a nonporous wheel.

 

[eKretz]

Looks pretty good, nice job.

 

[richard newman]

Okay I just learned my lesson and saw the chuck start to deform from heat. I am now taking smaller depths of cut (0.0005”) and slower table travel. That was scary, it started to move quickly.

How hot are we talking about to cause deformation?

 

[eKretz]

How hot are we talking about to cause deformation?

It's the rapid buildup of local heat that causes the trouble. It can get up over 500°F readily, as evidenced by blue or even purple discoloration due to heat in "burned" areas. A second or two later the heat has dissipated into the cool metal nearby and is almost room temperature again. That heat causes enough near instantaneous thermal expansion and force against the colder surrounding material to yield the steel or iron though, causing a permanent warp unless it's ground back out, which can take quite a lot of material removal to accomplish. Same principle is used for torch straightening.

 

[jwmelvin]

This wasn’t showing discoloration so I thought it was fine. (You can see how it was going in the closeup video above.) But when the passes started removing material along the whole length, it apparently heated enough that I could see the depth of cut start to increase. I knew what was happening after one or two passes but killed the throttle instead of waiting for the wheel to finish a pass so I could stop off the chuck. Hence the burn mark.

I think I was scared after that and spent a bunch of time doing passes that didn’t remove material, and when I did, the porous wheel was too soft to make it across without breaking down. Switching to the regular wheel, I took two passes at 0.0004” downfeed each and got what I have here. The chuck doesn’t appear to have been permanently deformed.

 

[eKretz]

You don't actually have to burn it to move it... That's just one way it often happens. And when it moves, it's more prone to a heavier grind, creating more heat, creating more movement, heavier grind, etc. That initial movement can happen just from stress in the material being relieved when it's removed. All of a sudden you've got a large hump in the middle or at both ends that wasn't there before, and often right after that GRRRRTT - burn mark and even more movement.

Grinding seems like a very simple thing, but as with any other machining operation, there are a lot of nuances that you discover along the way.

 

[michiganbuck]

rQt Op" (I think I was scared after that)
Likely the biggest and toughest SG job to do.
Good that you got scared. With a little heat and you may keep grinding to have a nice looking job and then find that when it cools it is .002 low at the center.
or have a sudden heat swell that sucks up into the wheel to causes a burn/warp. Mostly the burn causes a rapid expansion, and then a contraction, the contraction is the effect that warps the chuck.
Grinding a chuck dry you watch the sparks to know the space between them. when the sparks get closer together the next pass will likely sound different and you see and hear the grind not sound she same all the way across. You know you are in deep trouble. Some shop don't allow coolant on surface grinders. The worst chuck I ground dry had about .015 hollow/low at bump rail center. Don't ask me how they used it.

A weak mix of soluble oil make a very good chuck grind coolant, but you need really shake out your wheel after use

 

[cyanidekid]

I started grinding and it seems to be going okay. It will take a while. I have no experience but it seems reasonable. 0.001” depth, .020” stepover, 46 H Porous wheel.

The spark trail spreads across the wheel by the end of two passes, so I re-dress then.

View attachment 366679

Third edit: using more coolant definitely helps. Fewer sparks and just seems better. I have a hand spray bottle I’ve been using to supplement the mister.

rQt Op" (I think I was scared after that)
Likely the biggest and toughest SG job to do.
Good that you got scared. With a little heat and you may keep grinding to have a nice looking job and then find that when it cools it is .002 low at the center.
or have a sudden heat swell that sucks up into the wheel to causes a burn/warp. Mostly the burn causes a rapid expansion, and then a contraction, the contraction is the effect that warps the chuck.
Grinding a chuck dry you watch the sparks to know the space between them. when the sparks get closer together the next pass will likely sound different and you see and hear the grind not sound she same all the way across. You know you are in deep trouble. Some shop don't allow coolant on surface grinders. The worst chuck I ground dry had about .015 hollow/low at bump rail center. Don't ask me how they used it.

A weak mix of soluble oil make a very good chuck grind coolant, but you need really shake out your wheel after use

hey michigan , have you ever herd of using a copper chill plate or an aluminum heat sink between passes on a big part or chuck? a little water makes a pretty good transfer medium and can be wiped off for dry grinding to resume.
the cumulative buildup of heat in the not insignificant mass of the chuck without some means to get it out can wreck havoc on the grind, probably the main reason this can be so difficult, yes? so, if you can draw it out, keep the heat from building up, and work slowly its got to be better.
another idea is to use a thermal imaging device as you grind, to actually see what's going on there.
one more thing its important to understand is that the local heating from friction can easily and quickly completely overcome even copious flood coolant and burn locally, that's probably the main reason some shops don't allow it, it can provide a false sense of "it can't burn, its under water". wrong, you bet it can.

 

[michiganbuck]

Qt: (heard of using a copper chill plate or an aluminum heat sink? ) No, but have heard of spindle oil rag wipes, Calgon pink soap & water mix, alcohol, ammonia and water. and just a water wet rag wipe.
I usually use what ever coolant the machine uses, or a hand spray bottle of water and washing soda mix..(X not baking soda). The washing soda makes for anti rusting..
One trick is that if you discover heat first wait some time off the part, then increase the off the chuck at ends. and decrease the take or rate. *At first heat signal you up dial off the part(chuck).
To make the chuck last longer you place parts all about the chuck, not always on the rail center. And avoid small stones, the smooth side of a 6 or 8" 9 (chuck only) stone is best.

 

[richard newman]

This is very interesting, thanks guys. I think I dodged that bullet when I bought my Boyar Schultz 612 and dusted the chuck 25 years ago. I was a woodworker just getting into precision metal work, and another guy at the sale gave me some advice.

 

[ballen]

Flood coolant helps a lot with that because it keeps the temperature constant. The coolant mist that you are using isn't enough to keep the chuck from warming up. Is there a way to rig up a steady stream of coolant?

 

[jwmelvin]

Flood coolant helps a lot with that because it keeps the temperature constant. The coolant mist that you are using isn't enough to keep the chuck from warming up. Is there a way to rig up a steady stream of coolant?

Yep, I posted a picture of my flood coolant Monday afternoon. It made a huge difference.

 

[michiganbuck]

Q; (Is there a way to rig up a steady stream of coolant?) If you have no other then way hang a five gallon bucket with a 1/4" hose and gravity feed coolant. Use a calculator to convert that to metric if needed, something times something is the formula for converting, but close in close enough.
*Do test this/your gravity coolant device to know how much time it will allow.

Water, water with catalog coolant, un mixed coolant if according to instructions, water with some hack or homemade something, a coolant other than water or whatever coolant is used on the machine should do a fair job of it.. time and talent are just as important because one can still burn a wet chuck..

likely beer would work well, but if you are drunk enough to try beer you are in no condition to grind a chuck.

One time with not having a decent wheel I cut slashes to the OD of a wrong wheel by hand gashing the wheel on an abrasive cut off (parting) wheel, it workie just fine(wet).

 

[cyanidekid]

Q; (Is there a way to rig up a steady stream of coolant?) If you have no other then way hang a five gallon bucket with a 1/4" hose and gravity feed coolant. Use a calculator to convert that to metric if needed, something times something is the formula for converting, but close in close enough.
*Do test this/your gravity coolant device to know how much time it will allow.

Water, water with catalog coolant, un mixed coolant if according to instructions, water with some hack or homemade something, a coolant other than water or whatever coolant is used on the machine should do a fair job of it.. time and talent are just as important because one can still burn a wet chuck..

likely beer would work well, but if you are drunk enough to try beer you are in no condition to grind a chuck.

One time with not having a decent wheel I cut slashes to the OD of a wrong wheel by hand gashing the wheel on an abrasive cut off (parting) wheel, it workie just fine(wet).

haha! ill try beer next time, the evaporating alcohol may help with cooling, but I would only use coors light... anything else would be a waste...

"one can still burn a wet chuck" wisdom there.

 

[jwmelvin]

I used my freshly ground chuck to clean up the sides of a cheap cast-iron v-block. It came out with 0.0001” parallelism over the ~3x5” surface. I am happy, as it’s the first thing I’ve surface ground besides a block of steel and the chuck.

 

[michiganbuck]

I used my freshly ground chuck to clean up the sides of a cheap cast-iron v-block. It came out with 0.0001” parallelism over the ~3x5” surface. I am happy, as it’s the first thing I’ve surface ground besides a block of steel and the chuck.

Nice.
You might pick up an eBay angle plate, perhaps 3 x 5"with 1/4 or 3/8* tapped holes and make a bar that can be bolted on to it, with one side of it having a long V so like a long V block. Make an number of diamond holders, one tall/long so to be clamped to yore V block and also be your slide diamond for dressing angles to your wheel.
dressing an angle you rough it in with your stone and then they your slide bar diamond on a parked wheel to know where it will contact the wheel (with it wheel-pushed tight to the angle plate, and so not far out long from your angle plat support.
Solid angle plates are more accurate the ones with holes because of the chance a hole may have a grit to fall on the chuck.
You can make/rough-in V blocks with a 45*dressed wheel and the V block resting on the chuck. Good to grind all your fixtures dead square so they can all be used for block-ins.
Oh, bolting on the bar add a C clamp as every set up needs two clamp methods to hold secure.
A slide bar diamond dresser makes quick accurate angle wheels, and wheel corner angles like a 45* for making quick part beveled edges. Make or buy a sine bar and make a home made JoBlock for 45* if you don't have a set of gauge blocks.