Gunsmithing Lathe chuck backing plate maching trouble

[maccrazy2]

Hello everyone. I am hopeing someone here can shed some light on an issue I am having. I have a 12/36 lathe that I am trying to mount a new 6jaw chuck on. I ordered a new backing plate (D1-4) mounted it and tried to start machining it to size for the new chuck and cannot get it to cut cleanly at all. I am getting sparks flying from the tool. I tried HSS, carbide and an indexable toolholder. I also tried setting the tool at a few diffrent heights. When I am trying to cut there is alot of resistance and I really get showered with fine particles of metal.
I finnaly gave up and assumed the metal must of had some rediculous nickle content or something. It was stamped packistan if I recall correctly. So I ordered a second one from another supplier (shars) and tonight I gave the second one a go. It machines hard as well and I am still getting some sparking on occasion but not as much. It is not the same design or manafacture so I do not think the plates are the same. I verified that the tool is not at some odd angle in relation to the plate. I have 2 identical lathes and set up the first one without a hitch. the plate machined just like soft steel and the surface finish was great. I cut stainless on a daily basis without any issues. It appears to be a material issue but I really have never come across this before so I figured I would ask here and see if anyone has come across this before. Thanks Chris

 

[tfsron]

Re: Lathe chuck backing plate maching trouble


Sounds like it is time for the tool post grinder!

If a file glides across it, tool post grinder is the way to go.
If a file digs in, you have a set up problem with your tooling; you should be able to cut it with HS or carbide.

If you can't over come your set up problem, the tool post grinder always works.

Good luck
Ron

 

[300sniper]

Re: Lathe chuck backing plate maching trouble

all the d1-4 backing plates i have machined were some sort of cast iron and machined easily. it was more like a powder coming off than chips but the finish was great, even with the varying sfm on a large diameter facing cut. i get the import ones from enco. i can't imagine anyone using anything incredibly hard for a backing plate. since you are getting the same results with two different manufacturer's backing plates, i am thinking there is a tool or setup problem.

 

[maccrazy2]

Re: Lathe chuck backing plate maching trouble

I will check it with a file tomorow.
The first one I did machined like cast iron, very easy to cut and finish was good. That was several years ago and I cant remember who I got the plate from. I have a dumore toolpost grinder but I only have 2000+grit diamond wheels that I use on carbide. I am sure I can get some cheaper wheels for steel. I am just perplexed as I have never had issues like this before.

 

[AJ300MAG]

Re: Lathe chuck backing plate maching trouble

They make special carbide inserts for cast iron. Sounds like your in the "chilled iron" layer which is hard. Cheap casting...

Ceramic inserts will work better, as long as you don't have interupted cuts...

 

[baldie]

Re: Lathe chuck backing plate maching trouble

Cast iron, when knocked out of the sand moulds too hot, gets a very hard "skin" to it. This is whats happened.Cast iron is cheap no matter how its made...its not a lot different to pig iron. The surface finish depends on the time in the mould.

 

[LRI]

Re: Lathe chuck backing plate maching trouble

Ever think of slowing down your spindle speed?

Assume it's a tool grade steel hardened in the mid/upper 40's or maybe even low 50's.

Your SFM with say a grade 1125 carbide insert would be probably in the neighborhood of 75-125 SFM.

With a .0025/rev feed rate your looking at an RPM of around 60 for the outer end of it. Obviously it'll end up much slower (SFM) as you get towards center but at least it won't be the 4th of July when you cut on it.

Good luck.

C

 

[Victor N TN]

Re: Lathe chuck backing plate maching trouble

One thing to remember about machining castings. When they are putting metal into the crucible, they don't really sort the stuff. I have been turning castings on a lathe and hit tool bits inside the casting. The boss had a cow when I showed it to him. I'm not saying that's YOUR problem. But just file it back in your mind somewhere.

 

[scout67]

Re: Lathe chuck backing plate maching trouble

I agree with 300mag, if it is hardened then ceramic inserts work well. They are about the same price as carbide and will cut hardened material well if you don't have alot of interupted cuts. Just take light cuts at a higher rpm. My supplier said the chips should look like little red ribbons coming off the part. The diamond inserts work too but they are expensive.

 

[maccrazy2]

Re: Lathe chuck backing plate maching trouble

Thanks guys. I tried several speeds begining slow and tried increasing. I did not make it to the shop tonight to give it another go. I suspect you guys have touched on the issue, it may be case hardened. Will report how it goes. Thanks again.

 

[CDiPrecision]

Re: Lathe chuck backing plate maching trouble

it is most likely made out of cast steel. Not quite as soft and mushy as cast iron, and a bit harder to cut. Sounds like ur surface ft is too high. Tool should be on center, not above or below. I have cut 62 Rc D2 on a lathe so I dont see this being too much of a problem.

 

[Cheech]

Re: Lathe chuck backing plate maching trouble

slower speed.

 

[slabsides52]

Re: Lathe chuck backing plate maching trouble

If the surface is chilled iron, you will most likely need either a hot pressed ceramic or a CBN tipped insert to cut it, or ofcouse a tool post grinder. A good quality ceramic insert will work if there is not much porosity and no sand in the workpiece, and you have a good rigid set up. Cermaic inserts do not like shock, and require a rigid set up. CBN tipped inserts will handle more shock, and are usually ground with an edge prep that will reduce cutting forces and push off. However, they are pricy. If you stay with carbide, a good uncoated cast iron grade at a slower speed, 75-125 SFM, will probably be the best bet. Good luck, make sure your tool is on or a little below center.

 

[CDiPrecision]

Re: Lathe chuck backing plate maching trouble

Alot of the problem too is these little lathes just arent rigid enough. Everyone makes the mistake of buying a lathe to use some silly spider setup thru the spindle. Its a mistake.

 

[maccrazy2]

Re: Lathe chuck backing plate maching trouble

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CDiPrecision</div><div class="ubbcode-body">Alot of the problem too is these little lathes just arent rigid enough. Everyone makes the mistake of buying a lathe to use some silly spider setup thru the spindle. Its a mistake. </div></div>
???? I am not adapting a spider assy. I am changing the 3jaw chuck to a 6jaw on a 12/36in lathe. I use it to make some small plastic parts on occasion and the 6jaw holds better than the 3.
I was spinning at around 200rpm and when trying to machine the backing plate. With just .001 deep cut it is throwing sparks from a brand new indexable insert. Trying deeper cuts just throws more sparks. I will order some of the ceramic inserts this week and give them a try. Oh, the file (brand new) will put a small line in the material. I tried it on the other backing plate on my other lathe and it cut alot easier.