I've never turned anything this big & heavy and would like a quick pat on the back before I embark.
It's 13" OD, 2" thick steel. I'm making an A1-6 backplate for a 10" Adjust-Tru Buck 6-jaw chuck I got with the lathe.
The plan is to drill/bore a 3" (approx) hole in the middle, then switch back to my 10" Bison 3-jaw, grab the hole, and bring the OD of this plate down to 10". Then, grab that OD and rough in the features. Then, cut the taper, mount it to my spindle, and finish the machining on the spindle.
I know this is nothing compared to what some of you turn, but it weighs 80 lbs and would be a disaster if it came loose.
Thoughts, hints, atta-boys appreciated.
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[machinist] A quick safety check before I spin this, please
- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] A quick safety check before I spin this, please
- Date: Thu, 7 Mar 2013 19:38:34 -0500
A quick safety check before I spin this, please
http://www.practicalmachinist.com/vb/general/quick-safety-check-before-i-spin-please-261771/
Cast Iron
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A quick safety check before I spin this, please
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03-06-2013, 08:10 PM #2
Stainless
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Looks ok.make sure carriage clears the jaws sticking out.that would be ugly .make sure it's tight and go for it.
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03-06-2013, 08:11 PM #3
Plastic
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Use a very low rpm and plenty of lubricant and you should be fine. If you're still concerned, mill flats where your jaws will sit and clamp on those as they will later be machined off. Good luck and let me know how you make out!
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03-06-2013, 08:12 PM #4
Stainless
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Take the 3 jaw the 6 jaw and that bigas piece of plate and chunk them in the corner and learn how to use the 4 jaw and make some money with it and quit jacking off.
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03-06-2013, 08:21 PM #5
Hot Rolled
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Looks like you have at least 5/8" of jaw biting that thing. Crank it tight and go for it. Pull that scale and torch burn off with HSS or M42 and save yourself the price of a carbide insert.
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03-06-2013, 08:35 PM #6
Aluminum
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I agree with "Part of what Heavy Metal said" you can do all on the 4 jaw with better accuracy and safety.
Dont over tighten a 4 jaw with jaws sticking out that far, you can hurt your chuck!
I would rough your OD up to the jaws,face it , drill and bore your hole, and then if you can back face through the hole for dialing in . turn around in the 4 jaw and rough the other side. -
03-06-2013, 08:39 PM #7
Hot Rolled
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First thing to do is as Mr King mentioned...make sure carriage clears chuck jaws.
After that it's cake,as long as you tighten the crap out of those jaws it will be just fine.
What I would NOT DO is clamp on the 3'' ID to turn the OD with a 3 jaw chuck...BAD BAD BAD unless you take small cuts because for one the 3 jaw has no were as much clamping force as what you can do with a four jaw,plus leverage will be working against you turning a large diameter chucking on a small diameter.
If you go that route I strongly advise you make a plate larger than your hole with a big center hole in it and jam it against the part with your tail stock to keep it from walking off the chuck while working the OD.
You could machine 99% of it right there with that 4 jaw.
Go ahead and skin face the part and drill the hole and skin the od a half inch back or so.
After that move the part out of the chuck so you only about a half inch is in the chuck (IT WILL HOLD I PROMISE) and use the face and OD you just skinned to true it back up.
Machine to spec leaving .020" or so to finish machining after mounted on spindle.
Even with just a half inch in the chuck you can pull .100" to the side with no issues as long as you tighten the crap out of the 4 jaws.This will allow you to machine most of the OD on first side.
Machine first side,flip,chuck lightly on machine surface and half ass indicate it in useing scroll marks on chuck.Make sure jaws are tight enough part will not fall out but not so tight the hard jaws muck up the machined surface.
Back off ONE jaw at a time and put in a soft jaw (penny,smashed piece of copper pipe etc) between the part and retighten the jaw back down untill all 4 jaws are done.
I often jam a peice of wood or what ever against the part with the tail stock till I got a good bite on the part so it does not fall out and smack the ways.
Then indicate OD back in,use a last word indicator to reach thru bore and touch machined face on the back to true face in,do not assume that face is true by just setting again back of chuck jaws,it might be good,it might not.
Machine second side to spec and your done.
EDIT
Read post above about over tightening the jaws when they are stuck out a lot...he was very correct.
As long as you do not use a cheater on the chuck wrench and just give it a good grunt you will be just fine. -
03-06-2013, 08:45 PM #8
Titanium
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Since you're using a 4 jaw anyway, and assuming you know how to center a part with a hole, it might be prudent to start by running your pilot holes with a big DP or mill. That way you can run the small drills fast (e.g. the 1/8" at 1500 rpm), and get the hole big enough so that in the lathe your start with a 1/2 hole at 380rpm. By my calcs, an HSS boring bar for a 3" hole at 100 sfpm is about 125 rpm - a much more comfortable speed at 80 lbs than would be 1500rpm.
Question for the forum: would you go with an HSS boring bar to keep the speed and cost low, or would you run carbide at higher speed (using a 3x factor, a carbide boring bar could go up to 375rpm for the 3 inch hole, or about 1000 rpm for a 1 inch hole).
To the OP: If this is the first you've used the chuck I'd inspect the thing very carefully for cracks and such. Ping it with a screwdriver and see if you get a clear bell tone, or a dead thump.
You're caution is entirely well-founded, and because if it I happy to say I expect that you have a long, safe, and enjoyable career with your lathe. And if you are planning on just doing home-shop and one-off jobs, and don't need the extra non-triangulating holding power of the 6 jaw, your 4 jaw will be your go-to chuck. But this is an excellent project, and looks like fun. Enjoy and be safe. -
03-06-2013, 08:47 PM #9
Cast Iron
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The 3-jaw Bison is a very good chuck and I make lots of money with it.
Originally Posted by Heavey Metal
I have no idea if I'll like the 6-jaw Buck, but it's a $2500 chuck, and is basically brand new and was free with the lathe. This piece of plate cost me $35.
I have need of another A1-6 fixture; a 4-screw gunsmithing "chuck", so since getting the compound set to cut the taper is a PITA, I see utility in doing 2 at once. -
03-06-2013, 08:56 PM #10
Titanium
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I wouldn't spin that setup at 1000 RPM I can tell you that much Originally Posted by bosleyjr
. Here's what I'd do, for the center hole at least:
1. drill a 1/4" hole through (do this at the drill press I guess)
2. drill a 1-1/4" hole through
3. 1-1/4" boring bar with carbide inserts to bring it out to 3"
Now, I gotta ask, why are you making a 10" backplate out of a 13" diameter piece of stock? You're putting almost half that steel in the pan just to get it to size. Doing this by gripping the hole will be an exercise in frustration. You can't take a big cut out at 13" when gripping at 3".
If you really want to use that 13" piece, rough the OD with the 4-jaw gripping the outside, bringing half the length to 10, then grip that with the 4-jaw, and bring the rest of the OD to 10".
Safer and quicker than gripping with the 3" hole ... still putting >30# of chips in the pan though ...
Regards.
Mike -
03-06-2013, 09:04 PM #11
Stainless
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Just going to echo a couple of the most recent posters. Holding that by the 3" ID is going to be dicey in comparison to your first op holding it by the OD. Bolt it to a faceplate or make a mandrel or anything except trying to grab that by a 3" ID.
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03-06-2013, 09:14 PM #12
Aluminum
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Get a few chocolate bars. Make sure you are seen eating them. Make sure you are seen scratching the back of your head with the bar in the same hand while eating one of those bars. If all hell breaks loose then you can say that part of the chocolate bar fell down your back and into your underwear. Just looking at it from a different angle. ;-)
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03-06-2013, 09:18 PM #13
Cast Iron
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Excellent. I won't grab the ID of the hole, then.
Mike: I need thick plate because it'll be a Set-Tru style backplate. I didn't want to pay for a piece of jetted plate. I was at the metal yard picking up material for some paying work and they had this in the .45 cent per-pound bin... at $35 it was worth the extra labor of making it smaller.
Most circular "drops" have the spot cut into them where the waterjetter or torch "plunged" in, so I was happy to see a whole, 2" thick round plate. -
03-06-2013, 09:38 PM #14
Cast Iron
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See, it's THIS kind of knowledge and experience that keeps me coming back! Originally Posted by Scruffy887
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03-06-2013, 09:44 PM #15
Stainless
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Kudos for thinking enough of safety to ask before making chips. Those who caution about holding on the the 3 " diameter are spot on. Doesn't mean it can't be done but caution is the order of the day.
The blowhards who claim that the 4 jaw is the only way are just that, at the nicest. They suck. For all they know you have a years work lined up that is hexagonal. The 6 jaw adjustable chuck certainly has it's place. That's why they make 'em y' know. -
03-06-2013, 09:51 PM #16
Aluminum
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Never once did I say that the 4 jaw is the only way, nor did I say that the 3 and 6 jaw chucks are useless. Both have there place just not for roughing torch cut plate!!!! Originally Posted by tdmidget
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03-06-2013, 10:09 PM #17
Cast Iron
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Thanks.
I really can't speak to the 3/4/6 jaw debate. If I dial in my 10" Bison to a given diameter, it's a pretty remarkable workholder. The prints I'm usually work off of give me +\- .003" and I typically keep thing to way tighter than that on repetitive work.
As you say-- Buck makes and sells these 6-jaw chucks for $2500 (!) and that seems like it's worth at least getting up and running. I do some thin-wall stuff and also some soft plastic parts that might (might) work better in the 6-jaw. We'll see. I didn't pay anything for the Buck and I'm not married to the notion of it working, or not. I try to be results oriented and avoid preconceptions. That's MUCH easier when the item was free!
I know there's some real wizards with a 4-jaw, but when I can easily beat my tolerances with a 3-jaw scroll chuck, just bangin' along, I'm not dis-satisfied.
For true high-tolerance I will use the 4-jaw or the 4-screw chuck I'll also be making. I'm hoping to start cutting (rifle) chambers this spring and that's < .0001" work there IMHO. -
03-06-2013, 10:14 PM #18
Hot Rolled
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If I had a 6 jaw I would damn well get it prepped to be used... Thin wall stuff and plastics are 6 jaw territory. Just like all things in machining, you can get by with very little, but you can do it quicker/easier with all the accessories and widgets.
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03-06-2013, 10:23 PM #19
Diamond
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Screw the OD for now. Get all your ID work done and get it to where it will go on the spindle with the OD as-is. Do the OD work and final facing on the spindle instead of changing chucks, etc..
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03-06-2013, 10:25 PM #20
Cast Iron
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I'm in the 4 jaw camp, never leave to chance with a three jaw what you can have bang on with a four jaw. A 4 jaw has more holding ability with less damage to part surface, a lot more versatility and simple and quick to set up with a little practice. Granted a 4 jaw seems like a pain in the ass until you get the hang of it and a three jaw is useful but who wants to be changing back and forth. My 4 jaw stays on the machine and I do everything you'd use a three jaw in it and when I need a 4 jaw it is already on there. I'd never part with my 3 jaw, it's the best door stop I've every had.
Sorry about the 4 jaw rant, by all means get the 6 jaw set up. Make
sure your set up on the plate is as true and straight as you can get it
before you start, keep rpm down and get on with it. I'm thinking that
I'd bolt it to a face plate and do as much if not all the machining with
one set up.
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[machinist] A quick safety check before I spin this, please,
Lawrence London, 03/07/2013
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- [machinist] A quick safety check before I spin this, please, Lawrence London, 03/07/2013
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