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Black Forest
12-19-2010, 02:12 AM
In the description of how Sir John built his QCTP he says to mount the Tool block in the four jaw chuck and face all the sides. What is the advantage to do it on the lathe vs. mill. I would think it would be faster and easier to do it on a mill. Or what am I missing? Sir John are you awake yet?

danlb
12-19-2010, 03:15 AM
It was probably just convenient to do that way. I don't know of any advantage, assuming that you have both a lathe and a mill, and that the mill is not otherwise occupied.

Dan

ptjw7uk
12-19-2010, 03:47 AM
Probably quicker and easier as on the mill there will be no top clamping to hold it against the bed whilst on the lathe the tool will push towards the chuck.
My 2p
Peter

Black Forest
12-19-2010, 04:06 AM
That does not make sense to me. The work would be in a vise and the face mill pushing it to the bottom of the vise. The only difference I see is the work is turning on a lathe. On a mill the tool is turning.

joegib
12-19-2010, 05:03 AM
According to his reply of 9/12/2010 in this thread:

http://www.model-engineer.co.uk/forums/postings.asp?th=46016

John states "The design was probably done around 1980 and I think it was published in ME in about '85 or '87".

At that time a high proportion of UK model engineers still didn't have standalone milling machines. So, he described a construction technique that was accessible to all readers with a lathe rather than just those with a milling machine.

Joe

Davo J
12-19-2010, 05:59 AM
Unless you have a large face mill of fly cut it in one go on the mill, the surface finish will look better faced in the lathe.

Dave

Black Forest
12-19-2010, 07:04 AM
Now that David makes sense to me! I am making a 100mm square tool block and I have a 160mm face mill with ten inserts. I can face it in one pass. Ok just wanted to know.

airsmith282
12-19-2010, 07:39 AM
the advange on the mill would be if your fly cutter on your mill is to small and you want a flawless pass and all at once then the lathe would be the advantage so it could be done, the disadvantage is if your cut is not percisly the same debth you will not have a perfect square so you need to pay closer attention when squaring up all the sides on the lathe, but that s just my 2 cents...

J Tiers
12-19-2010, 10:56 AM
The lathe should face the whole thing in one cut, AND should face it flat or slightly concave.....

With the mill, you have to be certain the mill is "trammed" correctly, and that multiple cuts will meet exactly.... if you can't do it in one go. otherwise there may be flatness and convexity issues

Bottom line is that the lathe can do the job quickly and in a known good manner, if in reasonable condition. (not that the mill can't.... but there are more "if"s )

loose nut
12-19-2010, 11:42 AM
Lathe HSS or inserts are generally cheaper and/or can be resharpen in a home shop, endmills not so much. It's cheaper.

davidwdyer
12-19-2010, 11:51 AM
The one time I tried to face off on a lathe, the thing pounded so much that I quit and used the mill.

Perhaps the piece was too long.

To overcome the cost of end mills vs HSS I made this unit which I already posted once on this board.

http://www.johndyerco.com/Dad/FacingHead3.jpg

taydin
12-19-2010, 01:52 PM
With the lathe, won't the surface quality get progressively worse as the cutter approaches the chuck center axis? When facing large disks, I had a hard time getting a good finish this way. What I eventually did is doubling the speed of the lathe on the fly half way... But still, there was a little stub left at the very center and I needed to file it off :)

flathead4
12-19-2010, 05:57 PM
If your tool is sharp and you're are right on center, there will not be a nub. And you are right; you have to take into account feed rates with large stock.

TDmaker01
12-19-2010, 10:25 PM
of you look in the "Book of all Books" you will see in that in theory turning can produce a much better finish in the microfarreds(sp?) scale i think a mill says 63 and a lathe can go right down to even 16 i think.I could be wrong on the exact figures but i know according to the book a lathe is capable of a better finish.

I idealy the setup on a mill is easier but it takes a great skill to properly grind a bit for a single point cutter and far too little people have that skill (not saying john cant) to get a really nice finish and i mean far better than any endmill or carbide tipped cutter can produce.

my guess was because it was fun to set up and do on the lathe, and it theoretically should look better.