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loose nut
05-21-2012, 08:56 PM
Is there any reason to get/use a tool post grinder for grinding the OD's of cutters etc. or can they be lapped accurately enough to get the job done without grinding. This is for non-commercial home shop work .0005" to .001" tolerance (mostly .001"). I would prefer not to have to grind, usual reasons.

tdmidget
05-21-2012, 09:03 PM
Your post is somewhat cryptic. ODs of cutters? Not sure what you mean there.

loose nut
05-22-2012, 01:33 PM
Making accurately sized d-bits for one, shafts that fit into bronze bearings etc.

Will lapping take care of making parts with a fine close tolerance-ish finish as good (or good enough) as a tool post grinder would. Can I get by by lapping parts so that I don't have to grind. This is for very occasionally done work maybe once every year or two not everyday.

Black_Moons
05-22-2012, 05:54 PM
Making accurately sized d-bits for one, shafts that fit into bronze bearings etc.

Will lapping take care of making parts with a fine close tolerance-ish finish as good (or good enough) as a tool post grinder would. Can I get by by lapping parts so that I don't have to grind. This is for very occasionally done work maybe once every year or two not everyday.

A lathe with sandpaper and/or file can hold those accuracys, Once you get it to within 0.005" or so on the lathe.

loose nut
05-22-2012, 07:22 PM
I'm after a uniform smooth consistent finish. Can't really count on that with sandpaper.

oldtiffie
05-22-2012, 08:12 PM
Originally Posted by loose nut

Making accurately sized d-bits for one, shafts that fit into bronze bearings etc.

Will lapping take care of making parts with a fine close tolerance-ish finish as good (or good enough) as a tool post grinder would. Can I get by by lapping parts so that I don't have to grind. This is for very occasionally done work maybe once every year or two not everyday.


I'm after a uniform smooth consistent finish. Can't really count on that with sandpaper.

I am not at all sure that many home-shop TPG's will do any better than a fine sigle cut file and "wet and dry" silicon "cutting paper" will do.

It may take a bit of mastering but it can be very effective as regards size and finish.

Rich Carlstedt
05-22-2012, 08:50 PM
Yes, lapping will produce a superior finish
Here are some photos of my valve rods on the Monitor.
First the turned rods

http://i273.photobucket.com/albums/jj220/StationarySteam/Monitor%20Engine/monitor1472.jpg

Then I mount a Dremel sander ( the linear sander for chair rails) in my vise.
This sander uses a 1/4" wide clamp, so I mount a brass lap that was drilled in the lathe to size. Then you slit it and add abrasive ( valve grinding compound )
Introduce the rod and move it in and out and turn if you wish.
If the size is too large, just crimp the brass a little.
The sander reciprocates about 5,000 CPS with a 1/8" stroke approximately

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P5210138.jpg

Here is a photo showing the comparison.
Now this really works well for valve rods, because you want the abrasive direction to be the same as it is in the working direction.
For rods that turn, you need to lap in a radial direction for minimum friction

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P5210133.jpg

Notice that all tool marks have been smoothed and a nice low friction-constant diameter- surface has been created.
Now my packing in my valve glands will survive

Hope this gives you some ideas

Rich

GadgetBuilder
05-22-2012, 08:55 PM
I lap when I want an accurate size over some length and/or good finish. OD laps are fairly easy to make and use. My lap holder is a bit of 2" mild steel round, bored to hold 1.25" aluminum round. I have a length of 1.25" round so I cut a piece from this to make a lap, drill and bore to size and slit. A set screw keeps the lap from spinning in the holder and allows adjusting it to size and to accommodate wear. If the slot closes from wear, widen it and adjust - laps need not fit the holder closely. Most any soft material can be used to lap steel; aluminum, copper, brass, lead, etc.

I normally use 300 grit aluminum oxide with oil or WD40 but Clover valve grinding compound works well too and is easy to find. WD40 works to clean lapping compound off the work for measurements or trial fits.

It takes a little trial and error to find the amount to leave for lapping. The first thou or two lap off quickly because it is mostly tooling marks. When you get down to solid steel, lapping goes Much slower. The trick is to leave the right amount so the finish is good but it doesn't take a very long time to get to the target diameter. Finish improves with time as you lap, of course. As you approach final size you can stop adding lapping compound and the grit in use will break down and get finer, automatically improving the finish even further. Lapping compound gets on your hands but not the lathe although I put a couple paper towels on the ways just in case.

When lapping you'll easily feel differences in diameter of a tenth or two so you can concentrate on the high spots to quickly get the diameter consistent over the whole length. In addition, the work automatically gets more round from lapping.


http://bbs.homeshopmachinist.net/http://img543.imageshack.us/img543/9823/shopmadelaps.jpg (http://imageshack.us/photo/my-images/543/shopmadelaps.jpg/)%20%20Uploaded%20with%20ImageShack.us (http://imageshack.us)
http://imageshack.us/photo/my-images/543/shopmadelaps.jpg/

http://imageshack.us/photo/my-images/543/shopmadelaps.jpg/
http://imageshack.us/photo/my-images/543/shopmadelaps.jpg/
http://imageshack.us/photo/my-images/543/shopmadelaps.jpg/

Paul Alciatore
05-23-2012, 02:52 AM
I'm after a uniform smooth consistent finish. Can't really count on that with sandpaper.

Wanna bet? I can get to an almost mirror finish with sandpaper wet with cutting oil. Start with 120 grit and work down to 2000. Kick your spindle up to the highest speed. Use strips of sandpaper, "shoe shine" fashion. Very smooth and very consistent finish if you do it right.

Now, lapping WILL do a better job of controlling the diameter and roundness.

dian
05-23-2012, 04:47 AM
i use a piece of glas with the sandpaper on it to keep a constant diameter.

mcgyver, i assume you put the rod in the lathe and move the lap over it? will it also come out straight? i also wonder that about the cylinder laps you showed. do they produce a straight bore?

rich, the result will be only as good as the hole you made in the lap, right?

vpt
05-23-2012, 08:42 AM
I'd say it really depends on how far you want to go with the finish. I have gone as far as polishing on the lathe with a die grinder (using fabric buffing bit) while the part is in the lathe turning yet. Mirror finish.

Sometimes I just like the 600G or finer sand paper finish.

Sometimes a scotch bright/steel whole pad gives the finish I am looking for.

I find a lapped finish is dull and kind of rough but has its place.

I also like a nice clean file finish. Takes some practice but you can get a near mirror finish after doing a perfect stroke with a clean file.

I use a file to bring in the grease fittings I make to their .002" tolerance one end to the other. I found with the fittings that one stroke of the file will take off .001"

I wasn't totally concerned with a perfect finish, these were all filed in.

http://img821.imageshack.us/img821/3425/greasefitting018.jpg

http://img64.imageshack.us/img64/5171/greasefitting017.jpg

loose nut
05-23-2012, 02:11 PM
Now, lapping WILL do a better job of controlling the diameter and roundness.

This is what I was most interested in but I didn't get the point across. Dimensional accuracy and finish but not a high polish.

loose nut
05-23-2012, 02:13 PM
Yes, lapping will produce a superior finish
Here are some photos of my valve rods on the Monitor.
First the turned rods

http://i273.photobucket.com/albums/jj220/StationarySteam/Monitor%20Engine/monitor1472.jpg

Then I mount a Dremel sander ( the linear sander for chair rails) in my vise.
This sander uses a 1/4" wide clamp, so I mount a brass lap that was drilled in the lathe to size. Then you slit it and add abrasive ( valve grinding compound )
Introduce the rod and move it in and out and turn if you wish.
If the size is too large, just crimp the brass a little.
The sander reciprocates about 5,000 CPS with a 1/8" stroke approximately

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P5210138.jpg

Here is a photo showing the comparison.
Now this really works well for valve rods, because you want the abrasive direction to be the same as it is in the working direction.
For rods that turn, you need to lap in a radial direction for minimum friction

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P5210133.jpg

Notice that all tool marks have been smoothed and a nice low friction-constant diameter- surface has been created.
Now my packing in my valve glands will survive

Hope this gives you some ideas

Rich

Thanks Rich, I like that sander idea.

Rich Carlstedt
05-23-2012, 03:47 PM
rich, the result will be only as good as the hole you made in the lap, right?

No, The holes can be off (within reason !) , but laps are always made with material softer than the work piece. This is done for two reasons.
First you want the lap to absorb the abrasive, that is embed the sharp crystals(grit) into the soft lap, second, you want the lap adjustable to wear into the work.
Since the lap is soft, it will wear more, and in the process, pick up the profile of the work piece . As it adopts the profile, it causes the work to have fewer ridges on the surface . When the lap wears so it no longer has contact, you either recharge it with fresh (new )abrasive which will take up the space, or "resize ' the lap by crimping it ( closing up the hole)
All laps are slotted for this. Look in my photo showing the sander. Note the lap has a longtitudenal slot, and a cross slot. This allows for crimping when needed. The brass has "spring" so if too much it done, it will spring open
To ensure roundness, I rotate the valve rod as I move the rod in and out.
The very fact that humans have inconsistant manual repeating skills, causes the work to vary the rod positions, and that in itself produces extreme accuracy.

You see this in telescope mirror polishing, where the human interface produces more accurate surfaces, due to non-repetition of the polishing strokes

Rich

Mcgyver
05-23-2012, 05:03 PM
I find a lapped finish is dull and kind of rough but has its place.

]

just a function of the progression of grits....I've gotten a reflective surface by lapping up to 1000 grit....and you can go further