The machining and fabricating thread (mills/lathes and more here)

[corknose]

you never want a sharp tool when cutting metal. when i make my hss bits i make them to a point then radius them for a better surface finish.

[takai]

For carbide you do though. HSS on the other hand no.

[Sam-Q]

it wasn't that edge I was referring to though, I cant explain without a drawing

[takai]

Got my little parting off tool yesterday, and it works a treat. Needs a few little modifications, but other than that its great

[Sam-Q]

I thought you guys might get a kick out of seeing how I made an attachment to allow my lathe to grind my diameters. I was having some issues with surface finish on my 4130 (Cro-mo) steel as I mentioned earlier and I figured it wasn't going to be very good for when I do my bike spindles that slide through some bearings. So I had this loopy idea of using a very cheap 125mm pedestal grinder and mounting it to where the tool holder normally goes. Here is how I managed to make the adapting bracket:



It ended up being a whole lot simpler than I originally anticipated. But simple is good and it lets me rotate the whole assembly in degrees the same was as I normally would with a tapered cut on the tool post. It should be awesome to use as I can do all my normal lathe work and then when I am getting close I can undo the tool post, slide it off, put this in it's place and all under a minute. To bolt it in I made my own equivolent of a full length T slot with 2 layers of 5.5mm plate welded ontop of each other.


Here it is in action:




and the surface finish:




It works well but I still want to do the following:


- Make up an enclosure ontop of the grinder to hold the electrics

- Put a gaurd on it, probably modified for the most cover possibly allowing for good visability and access

- Make new plates that hold the disk in as the original ones are far from straight and cause the wheel to wobble, this seems to be the case on every grinder I end up with? It should run dead true after that.

-Maybe have a diamond dressing wheel that I can hold in my chuck to make it true, or even better on a magnet off the chuck so I can use it for other things as well.


The funniest thing is that it has cost me $20 for a grinder on special and about $1.50 in bolts.

Interested to hear what you guys think.

[orange32]

How bad was the surface finish before? Would it have been possible to just machine it to .03 - .05mm up and use some emery to polish it to size? I like what you have done, looks like it works perfectly.

Have you had any problems with chatter form the grinding?

[Sam-Q]

I don't have a picture of what it was like before but very "stingy". This is how it looked when I did try and get it close and use emery paper, it's still a bit rough though, more than the pic shows:



The reason was I would get it close and start doing nice fine cuts but it would still look like crap, but as discussed earlier in this thread it's probably not helping with my cutter. I found there is no chatter at all, even though the wheel is wonky, it's actually really smooth and progressive. What is a bit different though is that when I move it in the sparks keep coming off, as in I would of thought that I would move it in one position and it would grind till it was clear and then free spin, however in use sparks keep coming off. It will take some experience to get used to using it in regard to getting it to grind something to tollerence. I will take pleasure in using a micrometer instead of a vernia to see what it is.


I also posted this on the garage Journal forums (awesome bunch of guys), and some have talked about how doing what I did above while good will leave the very abrasive grid on my lathe to wreck it in a fairly short amount of time. I didn't think of this and after a good clean today I will look at amaking some temporary covers up out of plastic/rubber for next time. I also will look at hooking up my coolant pump, apparently it will let me have an even better surface finish.


Now Chris in regard to our chat about surface finish with tungsten carbide bits, I have been looking at catalouges and I think I hasve figured something out. Sandvic sell three grades of cutting tip for just about every shape available. They are for heavy cuts, medium and light, with worst to best surface finish for each. The shape of the rough cut is flat on the top, so it has no relief angle off the top of the cutter, the next one is the common one where it is flat for a short lip (0.5 to 1mm?) and then has a relief angle. The light cut has no shoulder and is an upwards angle which is pretty much like how any of us would sharpen a HSS cutter. Now what I suspect is that we are trying to get a good surface finish with the equivolent of a blunt edge on the cutter compared to the HSS cutters. I think they do this because the carbide construction is too fragile to have a sharp edge for normal use and hence it's only available on the light cuts. So I think it's only indirectly the material that causes the surface finish. SO what do you think guys, am I dreaming? Anyway I have some really nice chucky HSS bits from an ebay store called Stone-tools which I am going to sharpen and give a go.

[Sam-Q]

looks like my hunch with the tungsten carbide cutters was right:

[takai]

I suspect though that due to the size and weight of my lathe (in relation to yours) i can get away with using a 0.4 or 0.8mm radiused bit and still get a good finish.

[MAGIC MAN]

the machine has a massive part to play in it, not to mention the guy using it, the guy who taugh me how to use lathes and mills is to put it simply a machine. he is a freak of nature, and very switched on about tooling also. i'm sure i could ask him also about any queries you guys have, if you want some help