high material removal scraping technique?

Hi,
I'm scraping in my VN22L mill. So far, I've scraped in the column face, and
the ram's flat ways (top of the column) to perpendicular to the column face.

I've scraped the back of the knee to a good level of contact with the column,
and reasonable rough alignment with the column itself.

Now I have the knee back up on the column and the column vertical, to scrape
the top of the knee. The top of the knee excluding the scoring is well aligned
(perpendicular to the column face and parallel to the column top) within
.001" over 18" or better. So all I need to do with the top of the knee is scrape
"straight down".

The knee has bad scoring on the top dovetail, now that I've started scraping it
I've measured it to be about .015 - .020".



I decided to scrape this rather than have it ground, partly because I wanted to
monitor the alignments, minimize excess material removal, and generally cost and
logistics in having someone grind it.

However, I'm now removing say .015" x 24" x 9" of metal. The biax will do the job,
but fairly slowly. I'm tempted to try an angle grinder with a flapper sanding disc,
however I'm hesitant to risk digging a hole that could massively increase the metal
needing to be removed.

I think I'll try the sanding disc lightly in a small spot and measure how deep a "scrape" I
get with the sanding disc?

Then maybe a cross-hatch pattern like with a biax, periodically printing the knee with
the surface plate to monitor overall flatness?

How would you guys do this (aside from sending it out for grinding)?


Thanks,
Phil

I’d still use my Biax for a reasonably small area like you mentioned. Use a wide blade with as large a radius as you can without the edge scoring your work. Slow down the machine, lengthen your stokes, and lean on it. I can get almost a thou deep passes on softer iron. If your mill is a harder grade of Meehanite, my guess is you could do 5-6 tenths deep cuts. Slower than milling it, but doable.

L7

Some will say "but it ain't RIGHT", however, you might not need to do anything to the scoring if (as it seems in the pic) it is limited to a few places.

If there is material left to supply a good surface, then get that scraped for alignment, and if you like, you can fill the scored marks, or just ignore them and put on a good rubber cover. I'd fill them with an epoxy, just to keep grit out. The epoxy can be scraped down flush, it is not a bearing surface, just a filler.

If it is actually worse than it looks in the pic to me, then ignore the above and proceed.

lucky7 said:

I’d still use my Biax for a reasonably small area like you mentioned. Use a wide blade with as large a radius as you can without the edge scoring your work. Slow down the machine, lengthen your stokes, and lean on it. I can get almost a thou deep passes on softer iron. If your mill is a harder grade of Meehanite, my guess is you could do 5-6 tenths deep cuts. Slower than milling it, but doable.

L7

Click to expand...

Thanks. I tried the angle grinder and a brief touch resulted in ~.001" divots, but not
very controllable. No doubt with practice it could be improved.

So I went back to the biax, longest stroke length, wide blade, roughing in circles. after about 10-15 passes I'm down .005", so not too bad, and controllable.

-Phil

The scoring in the picture was after I'd already scraped just the scored areas to see how deep they went... the original situation was worse...

-Phil

why remove the scoring ? I have done a couple lathe cross slides over the years and a few score marks is just oil ways ,,

Hand work it, a Biax is cheating. A tool left best in the hands of someone with a very lot of hand work done while learning.
Handy and fast but so easy to overdo. Yes I do use one but not in love with it.
Angle grinder
You don't just clean up, it has to be square to others. Best finish in the world on one is worthless if not square and true.
Seen too many do nice and pretty but the machine runs no better than before all the effort.....
If I put a younger kid on this it would be hand work. No power tools allowed. Does not take that long, just lots of elbow grease and measuring.
A Biax has become a go to, go fast tool so a love and hate.
Bob

Nothing wrong in using an angle grinder to take out lumps of material when you need to imo (id leave your scratches tho), just be aware if youre new it can get you into trouble 10x as quick. Ive always used a cut off wheel but not the super thin types. Flap or sanding discs I found much less predicable.
Heres a look at what I did to a buddies grinder. A cris-cross action worked well to scoop out .012". Hand finished all surfaces once close.
GL

If you use the angle grinder, try a flap disk instead of a hard wheel. It may be more controllable, and less prone to digging grooves.

sfriedberg said:

If you use the angle grinder, try a flap disk instead of a hard wheel. It may be more controllable, and less prone to digging grooves.

Click to expand...

I found the opposite. Using a hard disc thats been trued worked best by a long shot.

D.D.Machine said:

why remove the scoring ? I have done a couple lathe cross slides over the years and a few score marks is just oil ways ,,

Click to expand...

I was concerned the scores (running front to back) would prevent even oil distribution.

The saddle's oil delivery is via a Z-shape from the saddle above:



And the scores (.020") were deep enough for chips to get dragged under the saddle.

you can fill them with Devcon ,,, I did that on a old 16" American cross slide ,

Brandenberger said:

I was concerned the scores (running front to back) would prevent even oil distribution.

The saddle's oil delivery is via a Z-shape from the saddle above:

View attachment 291173

And the scores (.020") were deep enough for chips to get dragged under the saddle.

Click to expand...

For all the TIME yer wasting yah could mill a pocket down the whole run of those scores and INLAY an alloy wear plate. Then mill. Then mini-scrape.

Or - better-yet?

Just make the acquaintance of a clan of the "chip brush" tribe, various conformations, plus arrange to be able to pressure-flush with a shot of lube good enough to CLEAR sneaky-creepy swarf & nasty coolant TF OUT ever' now and then... (cheap enuf, given yer wise to do it ANYWAY..) .. and...

"Run what yah got!"

Yah don't suppose that machine-tool went the last thousand power-on hours of its "ACTIVE DUTY" prior service life without ever making any parts to pay somebody's grocery-bill just because it was gone butt-ugly do yah?

Nossir. It WAS "run as what it had got.."

To get a idea of where you are with your angle grinder you can put your surface full of punchmarks
Soft blows or hard blows will give you some controle over the depth of the punchmarks Perhaps alter the angle ??? Now you have something to work to
I did see that technique once when in a mould of a gardenchair the seat had to become a bit thicker
The guys punchmarked the mould and went ahead with the angle grinder and flapdiscs


Peter

Done with scraping on the knee for alignment and reasonably good bearing. I had estimated
I was taking off about .008" from the underside of the saddle and somewhere around .025" to get below most of the the scoring on the knee.

Now I have the saddle (with freshly machined underside, awaiting turcite) sitting
on .053" of shims on the knee. This leaves room for a .008" feeler gage between the
mating surface of the saddle and the housing for the leadscrew nut and splined shaft.



The housing has about .008" of vertical play, so I'm planning on targeting a finished
thickness of scraped turcite + glue of .049" (midpoint of vertical play).

So somehow I ended up removing .049" of material more or less, rather than the .033" intended.

The alignment for perpendicularity to the column face is about .0015" in 24" (low toward rear), and parallelism with the scraped column top (ram mating surface) is similar.

All in all way too much scraping! But good exercise.

-Phil