Thread: Scraping Projects

Originally Posted by RayG

I read most of that thread on laser measuring of flatness, and it's mostly BS, with a smattering of good idea thrown in...

I can't say I'm surprised Ray. As mentioned, the author comes up with some stuff that is just great, but completely spoils that by sewing these acorns of wisdom in acres of BS.

Thanks for the information on the interferometer. I'll read more about that when I get a chance. I'm just drowning in unfinished jobs around here right now, and today picked up a 1300 C oven, so I'm keen to fire that up too. But the metrology side of things is fascinating ... frustrating, but fascinating.

Pete

CTC is promoting diamond wheels for $20. Are these any good for shaping carbide before lapping? If so what's the best grit to get? I have a number of lapping grits available.

Hi Bryan,
Can't help much with the wheels sorry, the one I have seems to me to be working great. The edge it leaves looks about the same as what Phils wheel was leaving, the problem is I cant read the grit size and I'm not sure I would trust it even if I could. Last I heard Phil was happy with his diamond wheel, he should have a real grit number for you.
I currently have two laps, 10 and 40 micro. I'm still not happy with the 10 micro as its been pretty easy to push through the grit and start hand turning the alum(though I must say it works really well for hand turning lol). One of these days I'm going to try lapping at 90degrees, but I'm not sure its a great idea If I'm reading the charts right 40 micro is 280 grit.

Stuart

Hi Bryan,

Here's a chart for diamond grit sizes. Lapidary diamond grit sizes and specifications for diamond wheels, laps, drums, and bits

I've got a couple of different grits in those syringes, but I haven't done much with them yet, I've been using a 400 grit diamond cup wheel... the setup described here...
https://www.woodworkforums.com/f65/sc...ml#post1398330

Hi Stuart, I've been thinking about a cast iron lap, or would that suffer the same problems as the aluminium?

Regards
Ray

Hi Ray,
I was all set to make cast iron laps but the advice I was given was that alum was the way to go. I can't remember why now. Alum may load easier but thats just a guess.

Stuart

Ray thanks, that's a great link. Except now I don't know which grit column to look at! Actually they line up pretty well don't they.

How are you finding the 400 wheel? The edge in your pic looks quite fine, and you're not bothering to lap, so the 400 must be more of a finishing grade? I might go for a coarser one. Cripes they're so cheap I'll just get a 150 and a 240. Or maybe 180 + 320. Then my lapping pastes will take me from about 600 - 3000 going by that chart.

I made my lap from iron, because that's what I had. Seems to work fine.

The cast iron lap I've made has never "caught" the cutting edge. I did however accidentally catch my scraper on the aluminium wheel at the scraping class once.
I find the cast iron wheel gives a slightly better edge too - but that is probably very subjective.
Joe

I too have too confess to inserting my carbide scraper tips into an aluminium (did I spell that right?) lapping wheel. This alone makes me wonder about a cast iron lapping disc, or, if not, being a hell of a lot more careful with my tip/wheel discipline. It only takes a moment's inattention to see those lovely little alloy flakes snowing down upon your forearm revealing that you lack the right stuff, shopwise.

Luckily I scored a nifty diamond grinder with indexing work tables. With any luck my inexact grinding days are over.

Greg

[ame=http://www.youtube.com/watch?v=y2AUew5Evxc&feature=digest_thu]Metal scraping: How to read the spotting - YouTube[/ame]

Hi Bryan,
Mostly makes sense to me(though I'm not sure that means much) certainly better than my drawing lol
I don't get the black dots. I see shiny silver dots. Only one other thing I would have liked was a high spot on the left hand side to "stop the master tilting". I know its just "a section of the area" but every time he lowered it I was waiting for it to tilt. Fussy aren't I? lol


Stuart

I had the same thought Stuart but then realised he is using a cross section and it might touch behind somewhere.

Phil

Bryan,
I reckon thast's the most detailed explanation I've seen so far,
Richard King tried to explain this with drawings in his video, but this interactive representation is excellent.
The above comments overlook that you are showing in the order of 2 or 3 mm of cross section, so tilting wouldn't be likely, since there are another few hundred spots nearby that could be higher or lower.
THe black spots are fine by me - yes, in reality thery are silver, but that's pretty difficult to represent in a colour - so black is OK. You explained in the text what they represented.
What would help - if you don't mind a suggestion - is to intersperse your video clip with blued up surfaces and show what they actually look like "in the flesh".

Well done,
Joe

Joe, I wish I could take the credit for that video, but it's the work of Nick Muller. Anyone not aware of his work - and interested in scraping - should take a look at his youtube channel. He has several pieces on scraping lathe components, and a series on a surface grinder rebuild that covers some alignment issues.

Sorry Bryan - I missed the very start because my connection kept stopping. I have been watching Nick's videos but missed this one it seems.
Good work you finding an pointing it out to us all!
Joe