Machining A New Back Plate

[Kroll]

Good morning guys,well I thought that while I'm home along I would start on machining my back plate for my 4 jaw chuck to fit my Sears/Atlas lathe.Long story short,I have never really use my lathe other than just playing around so I don't know what I'm doing.I started with turning the OD for the resists that will fit inside the chuck and thats as far as I can go cause I done burned up two of my Arthur Warner tips.Guys me not knowing, but I think the back plate is made out of iron not steel cause of the chips.Anyway I am taking small cuts to work my way to the point of facing the back plate that the chuck will seat on.Guys I have my lathe set at 625 and hand feeding the HSS cutter slowly.Giving the poor information here,can someone see what I'm doing wrong,maybe this is a job for carbide instead of HSS.But I thought taking small passes and slow hand feed all would be good.I was wrong,thanks for suggestions----kroll

 

[Silverbullet]

I'd try the carbide, if the cast iron is burning your high speed ones. Cast is sometimes pretty hard think it has to do with the impurities in the metal. When we ran a lot of cast sometimes during the cut we would run into hard spots the tool actually would screech and the spot would be very shiny compared to the rest . Take your time it will turn out right.

 

[coolidge]

I used to turn a ton of cast iron and typical for the smaller castings a batch of very hard castings would come into the shop from the foundry and send a whole box of carbide inserts to an early spark filled grave and that was with flood coolant.

 

[JimDawson]

I have my lathe set at 625 and hand feeding the HSS cutter slowly.

It also sounds like you are turning way too fast. Put the lathe in back gear and slow it down to about 100 or so RPM. If that works OK, then speed it up a bit.

 

[T Bredehoft]

Just this minute I walked from the shop to here, having turned a back plate to fit a new 4" 3 jaw chuck. The cavity on the back of the chuck is .160, I aimed at .150, quit when I got to .146. I wanted a 2.835 diameter, stopped when I thought it was right, measured 2.8357. The piece was pleasantly warm, so I calculated it would shrink .0005, making a very snug fit. I, like you was facing off cast iron with a HHS bit, but turning under 100 rpm. I think that was your problem, you were smoking the tips of the cutters. Sure, Carbide would cut it, I chose to take my time.

 

[RJSakowski]

Cast iron has a high carbon content: approximately 3% as compared to high carbon steel Depending upon its cooling history, it can be very hard (and brittle) White cast iron in particular is quite brittle and hard. It is typically used for as cast objects and not machined. When properly heat treated, carbon will come out of solution, forming graphite flakes and is known as grey cast.
Quality castings are usually made from nodular (ductile) or machinable (grey) cast iron. However, I would suspect that most of the castings for back plates now come from China and many times they are unconcerned about the quality of their products. I have run into hard spots in cast iron when drilling/tapping/milling. A recent experience with my Grizzly lathe comes to mind.
A good precaution would be to anneal the casting by taking to a high enough temperature to begin the annealing process and cooling very slowly. An oven capable of ramping would be ideal but heating to a dull red ( about 1600F) or just below the point where it loses magnetism, soaking for a while, and cooling in a bed of wood ashes should do the trick. I would expect this to relieve stresses in the casting as well.

 

[Kroll]

Lots of good ideals here,will slow it down some and see what happens.The back plate I purchase from Little Machine Shop about yr ago and just now getting some time to mess around----
Guys I email LMS asking about the instructions on how to layout the bolt holes and what to do first to the back plate and Chris just email them to me.When I purchase the plate I had the instructions but I loss them someplace.Thank you Chris------Carroll

 

[T Bredehoft]

My plate shrunk about .0003, I can start the chuck on the back-plate, and if there were holes in the appropriate places I'm quite sure I could draw it on to the back plate. But, since there are no holes and the mill to (locate and) drill the holes hasn't arrived, I'll wait. Considering: Should I draw it on and make it secure and totally concentric with the back plate, knowing that it probably will err .002-.003, or should I turn those .002 - .003 off the mounting diameter and indicate the chuck to .000 before screwing it down tight? A Quandary. I'll not solve it (if ever) until I can put the mounting holes in the back-plate.

 

[kd4gij]

As every one said you where turning way to fast 100 rpm or less. I made transfer screws out ov setscrews to layout my back plate. Chucked them up and used a 45deg tool to cut a point on them.

 

[T Bredehoft]

I made transfer screws out of setscrews to layout my back plate. Chucked them up and used a 45deg tool to cut a point on them.

Set Screws. The chuck is metric, all the set screws I have are SAE...Thought of that, but once together, the chuck and back plate will be hard to separate.