Thread: Surface Plate & Straight Edge Checking

In the thread "Surface Grinder Table Lubrication" I raised the aspect of ball and guide wear in my surface grinder.

I can measure the balls, but not check the rolling guideways for straightness, truth or wear.

My camel-back straight edge has industrial scarring and my granite surface plate has an unknown history with appearances possibly reflecting a hard life.
All good enough to check my steel surface plate, gauges and fixtures necessary to layout model steam locomotives, but with no guarantees at the levels required to check a surface grinder.

Is there anyone in the Sydney basin that has a prime reference plate and would let me check my straight edge against it ?

Anyone interested in visiting Kingswood to check my surface plate ?

I would certainly reimburse all associated costs.
John.

Originally Posted by electrosteam

In the thread "Surface Grinder Table Lubrication" I raised the aspect of ball and guide wear in my surface grinder.

I can measure the balls, but not check the rolling guideways for straightness, truth or wear.

My camel-back straight edge has industrial scarring and my granite surface plate has an unknown history with appearances possibly reflecting a hard life.
All good enough to check my steel surface plate, gauges and fixtures necessary to layout model steam locomotives, but with no guarantees at the levels required to check a surface grinder.

Is there anyone in the Sydney basin that has a prime reference plate and would let me check my straight edge against it ?

Anyone interested in visiting Kingswood to check my surface plate ?

I would certainly reimburse all associated costs.
John.

I'm not in Sydney, so I can't help directly, but if you blue the camelback and compare between the granite and the cast plate, then compare cast to granite. If all three agree, then you've got a straight line.

Or you could string some piano wire with right tension and look up the sag tables. A few on here could probably give you chapter and verse on doing wire based alignment stuff.

Once you are happy it's straight in x and y, you can skim the chuck and off to the races.

Ray,
Thanks for the suggestions.
This will not hold up the Surface Grinder, just something I have to 'getroundto'.

For the SG, I am thinking through a scheme of surfacing the top and bottom of a large(ish) object and measuring resultant thickness.

If the object thickness is constant, it is probably flat also.

If the object is flat, I can use it to test the granite and the straight edge.

John

Originally Posted by electrosteam

Ray,
Thanks for the suggestions.
This will not hold up the Surface Grinder, just something I have to 'getroundto'.

For the SG, I am thinking through a scheme of surfacing the top and bottom of a large(ish) object and measuring resultant thickness.

If the object thickness is constant, it is probably flat also.

If the object is flat, I can use it to test the granite and the straight edge.

John

Assuming you've skimmed the chuck, then the thickness will be consistent, but that doesn't mean it's flat. It could be bowed, or even wavy. If the table moves in a straight lines both x and y, then it will also be flat.

I think you will still have to have something that's straight/flat to compare the ground part with.

Ray

Ray,
I don't plan to use the chuck, but rather side clamps on a plate.

Research says that expected SG wear pattern results in the table sagging at the travel ends, kicking the other end (under the wheel) upwards.
This results in a ground surface that is bowed upwards in the middle.
If you do the top and bottom surfaces of a plate, the bow will be double in the middle.

If the plate measures constant thickness then, to a first approximation, the plate is flat.

That is the theory, I am sure there are many 'gotchas', such as waviness that can confuse the situation.

John.

Not the most accurate, but possibly a way if you've got a laser level?

Home Machine Shop: Laser Metrology

Dave H. (the other one)

Originally Posted by electrosteam

Ray,
I don't plan to use the chuck, but rather side clamps on a plate.

Research says that expected SG wear pattern results in the table sagging at the travel ends, kicking the other end (under the wheel) upwards.
This results in a ground surface that is bowed upwards in the middle.
If you do the top and bottom surfaces of a plate, the bow will be double in the middle.

If the plate measures constant thickness then, to a first approximation, the plate is flat.

That is the theory, I am sure there are many 'gotchas', such as waviness that can confuse the situation.

John.

I don't think that will work, you still need something straight ( or flat ) as a reference. Grinding a part is the final verification, if you are in the middle of a rebuild, then setting up a straight edge and clocking that from the spindle in both axes will tell you if there are any major problems that need to be addressed. Have you done one of the scraping courses?

So in summary, I can't think of any method that doesn't require a reference flat surface or straight edge. So it's back to your original question. The rule of 3.

Ray

Originally Posted by RayG

So in summary, I can't think of any method that doesn't require a reference flat surface or straight edge. So it's back to your original question. The rule of 3.

You could check the straight edge against an unknown plate. Check it once, flip it over support it from above, check again,.......... but at the level I think it would but ummmm fun....
The guy that made the granite CNC lathe/grinder with air spindles explains it in one of his you tube videos. Of course I cant find it ATM, I'm sure I'll find it soon enough
*edit* found it https://www.youtube.com/watch?v=cwdoUjynpEk start at 23.00

Stuart

Originally Posted by Stustoys

You could check the straight edge against an unknown plate. Check it once, flip it over support it from above, check again,.......... but at the level I think it would but ummmm fun....
The guy that made the granite CNC lathe/grinder with air spindles explains it in one of his you tube videos. Of course I cant find it ATM, I'm sure I'll find it soon enough
*edit* found it https://www.youtube.com/watch?v=cwdoUjynpEk start at 23.00

Stuart

His scraping is a bit iffy

I'll see if the link to a specific start time works...

https://youtu.be/cwdoUjynpEk?t=1353

This is the part of the video where he describes that straight edge measurement flipping, technique.

I would just check it with a king way type tool with the bit that sits in the V way the same diameter as the balls.

Originally Posted by RayG

His scraping is a bit iffy

Not sure it matters. You're only really interested in the local high spots right? Find them, mark them and measure them. Though that only gives you one line. I think you'd need more than that to prove a camel back is flat. Though depending on the sizes of the camelback and plate, once you have one line you could use that to prove the surface plate.... but to what level would you trust your numbers in the average shed? See.... fun

Thanks for all the suggestions - lots of research to be done.

In the meantime ....
The SG is back together and doing its thing.
At first I was concerned that the very low friction in the table travel would be a problem, but a couple of old toolmakers reassured me that manual SGs in toolrooms were low friction.

The table passed a quick DTI run-through test, the chuck went on with stringent cleanliness to the table but without bothering with a top check.

Did a couple of blocks parallel, MS and CI, both micrometer all 4 corners to <0.01 mm, good enough for me for now.

Other concerns have arisen that I describe in other threads.

I good friend has got a very good cast surface plate so, as suggested, I will be doing some multi-plate/straight edge comparisons to see if I can convince myself that everything is good.
John

Originally Posted by electrosteam

Did a couple of blocks parallel, MS and CI, both micrometer all 4 corners to <0.01 mm, good enough for me for now.

What size were the blocks?

MS was about 100 L x 30 W x 10 D, CI 80x50x30.
Chinese micrometers.

The finish had a regular scalloped appearance, but good enough for a first test.
Wheel was 170 x10 mm, not dressed and run at 2950 RPM.
No coolant, step-over about 2 mm with what I would call medium traverse speed.

I will work on improving surface finish, then finish the blocks off flat, parallel and square to be used as mark-out aids on the surface plate.

I already have decided I don't like the control panel in its original location, LHS below the table.
As the SG will often be used dry, the dust would become a problem.
Re-locating the existing control panel doesn't seem achievable, and I may have to get a special made to fit somehow on the RHS/mast area.

John

Originally Posted by electrosteam

MS was about 100 L x 30 W x 10 D, CI 80x50x30.
Chinese micrometers.

The finish had a regular scalloped appearance, but good enough for a first test.
Wheel was 170 x10 mm, not dressed and run at 2950 RPM.
No coolant, step-over about 2 mm with what I would call medium traverse speed.

I will work on improving surface finish, then finish the blocks off flat, parallel and square to be used as mark-out aids on the surface plate.

I already have decided I don't like the control panel in its original location, LHS below the table.
As the SG will often be used dry, the dust would become a problem.
Re-locating the existing control panel doesn't seem achievable, and I may have to get a special made to fit somehow on the RHS/mast area.

John

John. Get that diamond out and dress the wheel!! Good to hear you have it up and running.

DH