Granite sanding plate?

[BillBaker]

Doing some research on valve body rebuilding I saw a video (can't seem to find it now) showing they wet sand the valve body cases to get them straight and true again because they can become prone to warping over age causing the valves to not operate properly and even leakage. They did say it was a granite block or plate used. Anyone have any idea where to get these? Google doesn't seem to find any answers for me..

 

[Bill Lins]

Try your local monument (grave marker) dealer. You might also try places that make granite table/counter tops.

 

[XJman]

How flat does it need to be? Typically in machine work a granite plate is extremely flat. Much flatter than any generic piece of countertop or grave stone. They are lapped to less than .0001" on the surface.

 

[Wayne M.]

McMaster-Carr has everything you need. Great phone app too.

 

[Wayne M.]

McMaster-Carr has everything you need. Great phone app too.

View attachment 101595

 

[CRodi]

https://www.traverscanada.com/search.aspx?keyword=surface plate

How about these guys?

 

[CRodi]

https://www.traverscanada.com/search.aspx?keyword=surface plate

How about these guys?

 

[Wayne M.]

Travers is good too, but like Grainger, some need a corp account. McMaster deals with anyone.

 

[XJman]

Just from a machinist standpoint it would hurt my soul to see someone use a granite surface plate as a sanding block.

Before you buy new shop around the used market. You may be able to find a cheap used one that's out of calibration date that's close enough for your purposes. Same with lapping plates. Be sure the plate is softer than the material you are lapping. You need the abrasive to be captured by the plate and not by your part.

 

[BillBaker]

Great information guys, thanks for all that input. I'll check into all the above mentioned.

 

[HHhuntitall]

I have to presume you're referring to the transmission valve body... in that though, why not check it out, first? A quality straight edge and a feeler guage should do wonders to check it.... Or even perhaps have a machine shop check it? They resurface flywheels for $40 for me, and can usually get a block within a few thousandths all the way across... I'd think a valve body would be easy, too, were it found to be out of spec. Heat plays a large part of distortion and warpage, lets not forget. There are a lot of bolts in that valvebody, so it would have to be pretty warped to be out of spec enough to leak much. Then there's the factor of the transmission housing itself.... For the cost of a granite plate, it might could be done easier and cheaper.... just a suggestion, of course....

 

[ntsqd]

Easiest and lower cost than most lapping plates is to use a thick piece of glass with some crocus cloth on top of it. A previous employer, a former tool & die machinist, taught me that trick. I bought the 3/4" thick piece we use at my work for 'scooting' things flat from McMaster.

 

[akhappyjack]

A flat piece of glass and 320 wet dry is what I used,with a little solvent then check with a machinists straight edge

 

[SSage]

Just get a flat plate and wrap it in Emory cloth, start with coarse, then use the fine.

Must not take much to true them up? Sanding would get a lot of grit stirred up, seems like a mill would be better. Never really thought about it though. If the whole thing warps, I wonder if you could hold it on the sides. It's been awhile since I've seen my VB.

 

[ntsqd]

A mill can't get it flat enough without a skilled operator and a large OD insert cutter. Fly-cutting it isn't going to work very well, AND you'll be altering what may be a very critical dimension by easily .001's of an inch rather than the maybe .0001's of an inch that scooting it will. If you can't scoot it or lap it flat enough it is too warped to use and should be replaced.

 

[SSage]

A mill can't get it flat enough without a skilled operator and a large OD insert cutter. Fly-cutting it isn't going to work very well, AND you'll be altering what may be a very critical dimension by easily .001's of an inch rather than the maybe .0001's of an inch that scooting it will. If you can't scoot it or lap it flat enough it is too warped to use and should be replaced.

Makes sense, I didn't realize we are talking .0001.

 

[akhappyjack]

320 / 400 grit was shown this trick by a old transmission man. just keep the paper clean, I've fixed many 727 C6,4 valve bodys,governors usually when a valve bodys are warped the vb bolts are not tightened in a sequence, I start in the middle and work my way out works for me. And always clean the valve body out

 

[Removed at users request]

Lapping plates and glass are the only plates you should use. Lapping compound is the only true compound for lapping you should use. Lapping plates are the best though as they are specifically designed for this with the use of the lapping compound. Before you lap anything ensure that the plate is square with the world. Used plates can be worn from a lot of use. A straightedge with feeler gauge to check. Even better is a flashlight. Just put straightedge on plate and shine the flashlight at the edge and the plate. If you see light shining between the edge and the plate you know it is worn and not good. Do not use.
Important to note that when lapping use figure eights. Do not lap in circles or straight back and forth. You will get a more harmonious outcome with your finished product by using figure eights. Do not apply heavy pressure to the piece. Just light pressure and check often. Do not want to remove anymore metal than is necessary. Care and caution and patience are key to a successful product outcome. Lapping plates were used, back in the day, when rebuilding injectors. Lapping plates have grooves in the surface forming many little squares. These little squares are what makes the lapping plates work better than anything else. And that is precisely why you want to lap in circle eights on a lapping plate. Circle eights are the most efficient method of obtaining that coveted harmonious outcome.

 

[ntsqd]

Along with above, I periodically rotate the part in my hand so that I'm not pushing down in the same locations all of the time.

Even when using crocus cloth or fine wet/dry on a glass plate, use the figure 8 method. It takes some getting used to, your hand naturally wants to go in a circle. Be patient, you'll get it.

I use a light oil (Marvel, PB Blaster, whatever is handy) with ferrous metals and WD-40 with aluminum alloys to keep the crocus or wet/dry from clogging up.

 

[XJman]

Oxtoolco on YouTube has a fantastic video talking about lapping. Check it out.