Heat or Chuck Dressing Time?

[G-ManBart]

I'm just looking for a sanity check here. I bought a surface grinder a while back that needed just a few things done to it....new ball cages, restring the drive cable and new wheels. I took care of all that and started to teach myself how to be a bit of a grinder hand. The one thing I held off on was grinding the chuck because I understand that to be a bit of a challenge for someone new to grinding, especially so without a coolant setup. Still, I was getting more than reasonable results and no major issues.

I recently decided to make some parallels for my shaper vise when I noticed they weren't coming out as level as I would expect. I started with two pieces of cold rolled mystery steel that was approximately 1.25" x .875". I started with them laid flat to work on what will be the "sides" of the parallels since those surfaces aren't as critical as height. They were roughly centered in the middle of the table both X and Z directions. I marked the pieces so I knew the orientation on the table, and took the measurements in the pictures with them oriented the same way they were when mounted on the table.

I started with a fresh diamond dress of the wheel, and then took roughing passes that were around .002" deep with about .035" steps each pass. After I was sure I was making contact the whole length and width of the two pieces I dropped to a .001" pass, then to around .0003" with a smaller step of around .025" and would do several passes until it sparked out. It was probably one or two passes at .002", one or two at .001 and then a couple at around .0003". I put a fresh dress on the wheel, flipped the parts and repeated the process.

The wheel used is a new CGW 7 x 1/2" 46I.

As the picture shows, the two pieces are .0004" thin at the center suggesting the chuck is high in the center, but otherwise pretty consistent...at least within the range of my ability to measure carefully. If I measure additional points between the ends and the middle there is an obvious slope, so it's not just one high spot in the middle causing a problem.

I never removed the chuck to clean under it, and I have no idea how carefully it was torqued down to the table. Visually, the chuck looks pretty good (made in Taiwan, so I'm guessing 80s) with no major issues and I do run a stone over it before mounting the dresser and parts. If it was heavily worn I would expect it to be low in the middle causing parts to be thicker in the middle.

Since I was grinding dry I could feel the parts get a little warm, but nothing dramatic. Still, heat will make things move, so it has to be considered. Does this sound like it's time to grind the chuck or add coolant and see what happens first? Either way I'm putting together a system with a 5 gallon bucket, coolant and a Little Giant submersible pump anyway since the machine is set up with a coolant tray and a drain.

Thoughts?

Machine when I unloaded it:

Picture showing the measurements:

 

[mattthemuppet2]

Could the parallels have warped upwards slightly as they warmed up?

Would holding a DI on the head and running the chuck underneath it tell you if there’s a bow in the chuck?

 

[G-ManBart]

Could the parallels have warped upwards slightly as they warmed up?

Would holding a DI on the head and running the chuck underneath it tell you if there’s a bow in the chuck?

I wondered about the heat causing a warp like that, but the fact that they don't taper seems to tell me that wasn't it. If it was just warping due to heat I would expect the warp to increase as the cut went along and put more heat into the piece rather than increase and then decrease.

I watched a video by one of the grinding experts and he suggests that using a DI won't tell you anything if the table is moving in an arc...the indicator stays in the same spot and the table doesn't move relative to the indicator even though it's not moving in a flat plane. If you could fix something to the head that would let you sweep an indicator across the table that probably would work...not sure how I could manage that with tenths accuracy given what I have available. The grinding expert pretty much said the work would tell you if the chuck was flat, but he was referencing a setup running flood coolant. He even runs the coolant over the chuck for a period of time to equalize the temp of the coolant and the chuck as much as possible before starting on the work.

 

[toprecyler]

I am far from being very knowledgeable in terms of grinding, but can you try to put the pieces end to end and do a longer stroke of the table? Maybe move pieces to one side of the table instead of the center. Check to see if the results are similar?


Sent from my iPhone using Tapatalk

 

[Dabbler]

Grinding soft steel like that is much more difficult than grinding hardened stock. If you were to try this on some Rc55 or 60 material, you would have a very different experience, coolant or no.

I don't use coolant about 1/2 the time, here are some tips:

Take very small cuts in soft material, 2 or 3 tenths max. (better 1 tenth) use a very slow, steady speed. Creating a lot of sparks is also heating the material up a lot.

Wait 10 or 15 seconds at each end of the travel for the heat to equalize across the work.

Dress your wheel *often* soft material loads your wheel while at the same time pulls out your grit.

If you have the option, use the hardest ruby wheel you can afford, with a reasonable grit size: 30 grit ruby wheel in L or M hardness. I wouldn't even try what you are doing with a 60 grit wheel or more.

That is all the basic stuff off the top of my head. - It has been 20 years since I have ground anything less than 50 Rc.

 

[woodchucker]

I'll add consider using the radiac ruby stone. I have the RAA462, It leaves the best finish on hard and soft material. I love the open grain. It runs cooler. I learned about it from Steve at Solid Rock Machine https://www.youtube.com/@SolidRockMachineShopInc/videos

I think this was the video that made me try it, I've never been disappointed. I still use my white ALOX for hard, but the Ruby does it too, runs cooler, and can hog off material. I run mist or flood. On my grinder flood makes a royal mess.

 

[Rich Carlstedt]

One of the most difficult jobs to do on a Surface grinder is making straight edges
The metal will bow , so the secret (sort of) is to flip the part , top-bottom -top - ect to even
out the stresses induced in the metals structure .
As you flip, you take lighter passes --which inturn produces less stress on the surface .. you want top and bottom of the straight edge having equal stresses..

Having the center thinner is a function of heat buildup. The ends cool faster , while the middle cannot grow lengthwise and that means vertical into the wheel, which in turn removes more metal in the middle of the part. I would never try to grind parallels dry, it is asking for trouble IMHO

 

[pdentrem]

Also don’t lay the pieces inline with the wheel. Thin materials should be at an angle. Light cuts.

Most of the wear in the ways will be in the center portion of the travel. Try to set up on the ends of the chuck and if you can move the chuck over to one side as much as possible. Indicator will show nothing about the taper of the ways.

SG are sold off when they are worn out, and we buy them for our home shops due to their precision capabilities. Companies are not willing to scrap the ways so rebuild the machine, and the machines are written down on their books over the years of use.

Unfortunately or fortunately most of us don’t need the ultimate precision that a new SG can give but can tolerate a worn machine.

 

[G-ManBart]

Grinding soft steel like that is much more difficult than grinding hardened stock. If you were to try this on some Rc55 or 60 material, you would have a very different experience, coolant or no.

I don't use coolant about 1/2 the time, here are some tips:

Take very small cuts in soft material, 2 or 3 tenths max. (better 1 tenth) use a very slow, steady speed. Creating a lot of sparks is also heating the material up a lot.

Wait 10 or 15 seconds at each end of the travel for the heat to equalize across the work.

Dress your wheel *often* soft material loads your wheel while at the same time pulls out your grit.

If you have the option, use the hardest ruby wheel you can afford, with a reasonable grit size: 30 grit ruby wheel in L or M hardness. I wouldn't even try what you are doing with a 60 grit wheel or more.

That is all the basic stuff off the top of my head. - It has been 20 years since I have ground anything less than 50 Rc.

Thanks.

I'm trying to wrap my head around the idea of waiting 10-15 seconds at the end of travel. For a 12" long work piece 2.5" wide like this was, it would be 30 minutes of waiting if I was taking .020" steps each pass.

A ruby wheel is on my list to add soon.

I actually have tool steel and alloy steel I can heat treat to well over 50 Rc so I might make a test piece to work with.

 

[G-ManBart]

I'll add consider using the radiac ruby stone. I have the RAA462, It leaves the best finish on hard and soft material. I love the open grain. It runs cooler. I learned about it from Steve at Solid Rock Machine https://www.youtube.com/@SolidRockMachineShopInc/videos

I think this was the video that made me try it, I've never been disappointed. I still use my white ALOX for hard, but the Ruby does it too, runs cooler, and can hog off material. I run mist or flood. On my grinder flood makes a royal mess.

I've watched several of Steve's video and he's who I was referencing earlier, I just couldn't remember his name. I'm going to try the ruby stone he recommends.

I was looking at mist systems as well, but pretty much have what I need to make a flood system on hand now. Then I was reading about not creating the mist stuff and went down a rabbit hole of mist versus flood and I think I burned more than a few brain cells trying to sort out all the opinions on them.