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07-25-2014, 10:42 PM #1
Using a grinder to 'scrape' a hardened part
Today i tried to scrape a parallel but found it was damn hard, would have taken ages. It was one of 4 at 15" long, ebay bought, all of them bannered a good .0008 or so.
With need being the motivator i got the grinder out. Setting up well down wind from the plate I got stuck into the smallest one (ive an extractor that could suck an elephant through the eye of a needle).
The first side done. (retouched it after the other side was completed)
The flip side. The blued area is around .0008 from 0.
3rd rub (i think)
Close up of the cheapy grinder and general butchering.
All up im very happy with how it turned out, am keen to explore further with a view to roughing work / working with hard materials etc. Made light work of the job, can imagine it to be very quick when you have some methods dialled in.
07-26-2014, 07:39 AM #2
we would either blanchard grinder or do on a CNC mill.
we call then trim blocks. trim blocks mounted on table and are bolted down and a .001" is taken off to make sure the trim blocks are flat and parallel to machine axis. Then part is mounted on the flat trim blocks and machined with carbide endmills or facemills. of course milling hardened material you take a low depth of cut and lower feed rate but we mill harden material quite often.
i can see having to be careful not bending a curved part as clamping to flat trim blocks. similar to a magnet of surface grinder wanting to bend curved parts flat to table when magnet turned on.
feel free to grind or scrape surface. i am just saying plenty of places have learned how to mill hardened materials flat to 0.0002" tolerances at 10x the speed. i am not saying it is fool proof but like i said plenty have figured out how to do it.
when using .001 and .0015 feeler gage material it is easy to get a .0005" difference if shims are needed. if long skinny part is curved .0005" when unclamped then yes that could be a problem getting last .0005" curve out. i suppose then you would have to scrape or lap part
07-26-2014, 08:36 AM #3
Thank you for sharing this and with pictures! Looks very good! Looks like 30 / 40 PPI with 50 % contact.
I was inside a plant teaching a scraping class and they asked me to take a look at a CNC lathe out in the shop. We threaded our way out the machine as it was burried in the middle of the shop. The hardened ways were worn and they could not hold size. They wanted to know if they could scrape them and I said no...They said they would have to shut down production for the plant to disconnect and move dozens of machines to get the machine out to be ground. I said I could grind them better then they were and they went for it. We used small air operated angle grinders with 2" sanding disks.
We did basically the same thing your doing Demon and it worked. We were able to sand/grind the bed to .0003" plus some lapping compound on a small cast iron lapping plate, 2" x 2"x 6" long with grooves in it and diamond lapping compound. There were a few deep screw ups but the majority was ok.
I like how ingenious your air grinder scraping is. Many times one can find some very interesting ways "to skin a cat" by experimenting with new tools and idea's. :-) It make things fun :-) Rich
07-26-2014, 12:03 PM #4
I read someone's account of doing the same thing years ago by using Cratex wheels in a die grinder in the same process. The choice might depend on what speed or hand control felt best or just what tools were available. Perhaps with a fine sense of humor one might be able to fake flaking crescents with a grinder.
07-26-2014, 02:36 PM #5
Did that too once Used a stick in one hand held above the surface and tapped the grinder on the stick and from thereone to the surface
With me it was just cosmetic but it worked better as expected
peter from Holland
Edgar10937 liked this post
07-26-2014, 04:14 PM #6
It's how I finished the hardened bed of my HLV. I used truncated cone mounted points and then bullet shaped Cratex points on an electrical die grinder. Lapped to get desired bearing.
It's a bloody site easier than trying to plough though 60HRC steel with a scraper!
RC99 liked this post
07-27-2014, 10:02 AM #7
not for nothing but it seems time consuming with little profit doing anything hand held.
next somebody is going to say the have hand filed a 3 " diameter ball screw 20 feet long.
i am not saying there might not be a rare need for something hand done.
i just can not see many well paying jobs wasting a lot of time doing hand work.
got to be 999 jobs machined on a large machine to every one job done by hand
07-27-2014, 11:17 AM #8
The fact that better methods exist is not lost on us but it does not mean that the discussion has no validity. Thank you for taking the time to comment.
07-27-2014, 11:17 AM #9
Is good to know that the same lines of thinking have been employed by the folks with the expertise and experience, such as yourself. Got to agree with the experimenting sentiment too, keeps it interesting, and you never know what you gona learn from the experience, good or bad.
07-27-2014, 12:05 PM #10
I used a stone for bearing, just a cheapy that i keep lapped flat.
Im not here to say that this is the way this particular task should be done, or that it cant be done any other way. Personally ive no grinder or dead nuts miller, but i do have a 15yr old well used cheapy cut off wheel and an SH granite flat .
Cueball liked this post
07-27-2014, 01:20 PM #11
Back in the days of my apprenticeship(60 - 64 yes THAT long agp!!) we used a version of this on board ship to scrape in turbine case flanges that were so steam oxidized the scraper slid over it. Thing is, all we had for grinding was 7" air powered Bayflex grinders. They were too heavy and clumsy for this kind of work. The enormous wheel (comparatively) was very doifficut to spot with precision.
We were all fit and strong but after ten minutes our arms were falling off from the strain of holding a bulky clumsy 16 lb tool to high precision. It worked though. A couple hours of dabbing the grinder on blue spots got us through the oxide layer into clean steel and we could use scrapers so we could procede to a steam tight metal to metal joint.
Had we small cut-off style wheels on a die grinder, the job would have gone much quicker with less strain. However they were unavailable to us at the time so we did the job with brute force and awkwardness.
I bought a Proxxon angle grinder
PROXXON TOOLS: Longneck Angle Grinder LHW/E
some time ago based on a Milacron post. I bet that could work wonders on hard material. If I had a worn out hard way handy I could try it out.
07-27-2014, 01:59 PM #12
what was the indicated height difference between lows and highs?
I can see this working well for tooling like a parallel but wonder about it for linear bearing surfaces. The reasons is if high and lows are too far apart the the thin wedge of oil might not establish itself and you end up with asperities colliding through the film and rapid wear.
07-27-2014, 07:57 PM #13
"Asperities": new word, I was unaware of its technical usage and definition; very apt for this situation. Thank you, McGyver.
Last edited by Forrest Addy; 07-28-2014 at 12:44 AM.
07-28-2014, 07:31 AM #14
Probably more useful, I put a couple marks on a fresh surface.
Hard small radius pull scraper pass
I did try a pass on the DSG bed last night. Worked out pretty well although it feels much courser to the touch than the parallel did, all traces of grinder marks were taken out in the next 2 roughing cycles.
Spyderedge liked this post
02-09-2017, 03:53 PM #15
Did some grinding today as practice for a job I might have to do that involves hardened ways.
Funny, makes my hands look massive , 3" angle grinder, cheap as chips.
All finished up.
Just for lulz I did a little bit moore
Pics dont really do it justice, looks real pretty in the flesh. TIR around 0.0008
02-09-2017, 05:02 PM #16
I have done that with a very slightly rounded OD or cone point mounted wheel wheelwheel so the scalps were not very deep.. But your job looks great.
02-09-2017, 05:08 PM #17
That's a good TIR for ways. For the straight edge, I'd do a number of passes with a dremelloid and Cratex points to get down to lower numbers if possible.
02-10-2017, 01:00 AM #18
The late Harry Bloom from this board scraped at least two hardened ways on Monarch lathes that I'm aware of using his (and now my) Biax, do a search for "The Wreck" and "The Wreck update". Harry was a gifted individual and I miss his input here. While I have personally never owned a Monarch lathe I would always look out for his posts on that forum simply because he was so knowledgeable and freely shared that wisdom.
I believe RC did some experimenting with using a grinder on hardened material and it worked very well. He may be able to offer more input.
02-10-2017, 04:54 AM #19
Cheers fellas, still yet to try mounted points. Ive a sensible long shanked die grinder I could use so will give it a bash when ive a mo, can imagine itd be great for accessible fine work. That said, im a fan of depth for most stuff, inc reference surfaces. Bought the mini grinder cos I wanted to stay away from the air, + is feckin freeezing atm.
Used the same sort of 'dab dab' method Chris used in his video, used longer strokes when roughing and shorter strokes when breaking it up, much better technique than what I was initially doing. The curlys were just for fun but they do look cute
02-14-2017, 08:36 PM #20
Those bearing points appear to be too large and irregular. Try to even things out and the bearing area will last much longer and wear "straight down"
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