Author Topic: Building a New Lathe (Read 535500 times)

Homebrewer · « **Reply #400 on:** May 06, 2018, 11:37:53 PM »

Glad to see you pouring metal again. Can't wait to see this one running!

Sent from my SM-G950U using Tapatalk

awemawson · « **Reply #401 on:** May 07, 2018, 01:40:37 AM »

A bit of 'bondo' and it'll be fine

Seriously though I know the frustration of working without the right facilities. I remember when we moved here and all my tools were stored elsewhere the issues it raised

vtsteam · « **Reply #402 on:** May 07, 2018, 04:47:39 PM »

Thanks Homebrewer.

Don't give me any obviously workable heinous ideas Andrew! There's a can of Bondo in the shop.

.

No, no, get thee hence..!

awemawson · « **Reply #403 on:** May 07, 2018, 05:00:10 PM »

All right use Devcon aluminium putty and you don't even need to paint it, it'll polish up nicely.

vtsteam · « **Reply #404 on:** May 07, 2018, 07:59:03 PM »

I've decided to fill the entire casting with Zinc alloy. By re-casting!

So, second try, more comical than the first...... uh, well it started out good. I clamped a board to the pattern and drilled in from both ends to create a half hollow when taken apart. Then, you'll like this Andrew, Bondoed the rough wood finish that my paddle type bit left.

Fired up the furnace and placed the last casting back in the crucible, conditioned the greensand and laid the pattern into the drag, rammed, and rolled it:

vtsteam · « **Reply #405 on:** May 07, 2018, 08:07:57 PM »

A bit tight in there as you'll notice, above. But blithely continued on, rammed up the cope, pulled the sprue and riser bits, waited for a melt, and poured. The sprue stayed nicely choked until the riser filled, and then suddenly they both plummeted back down while zinc poured out the parting line!

Classic mistakes: too small a flask for the job, not weighting the cope down.

I had forgotten that zinc weighs a heck of a lot more than aluminum, and will definitely float a small cope. Well, I suppose it's possible I got away with it because I saw a small amount of the pour left in both cavities. But not very likely. Anyway, waiting for it to cool, so I'm posting this.

vtsteam · « **Reply #406 on:** May 07, 2018, 08:50:23 PM »

Looked pretty good when I first broke some sand away:

vtsteam · « **Reply #407 on:** May 07, 2018, 08:53:13 PM »

But no such luck. That's a pretty short sprue!

I also noticed the surface finish wasn't much to write home about -- my sand was a little dry. I've re-hydrated for tomorrows attempt. I've only been able to cast after work at 5:00 PM, so once a day is about the limit.

vtsteam · « **Reply #408 on:** May 09, 2018, 08:49:21 PM »

Third try this evening after work. I plopped sprue and riser right on top of the pattern. That put the two channels in from the flask edge, and put the hottest metal at the base of each for feeding the casting as it cooled.
Also weighted the cope down.

Much better looking pour....

vtsteam · « **Reply #409 on:** May 09, 2018, 08:50:54 PM »

Better looking shake out, too.

vtsteam · « **Reply #410 on:** May 09, 2018, 08:53:45 PM »

Top looks good. I hope tghere won't be any surprises when I cut the sprue off -- deep hole in the sprue -- I watched it sink down over several minutes. It was overflowing at the start. Zamak shrinkage is amazing compared to aluminum and cast iron.
Anyway, fingers crossed....

vtsteam · « **Reply #411 on:** May 10, 2018, 09:32:15 PM »

No such luck. A fairly deep hole directly under the sprue.

vtsteam · « **Reply #412 on:** May 10, 2018, 09:38:46 PM »

This time however, I decided to try to repair it. The hole is nowhere near the bearings or cap bolts, and I could see the bottom. So I thought I'd just try melting a small amount of the same material, and pouring it into the hole. This is a lot easier with a low temperature melting alloy like Zinc. I figured there was nothing to lose, and the hole wasn't in a structural area anyway.

When I poured it full, I noticed immediate shrinkage beginning, so I topped up the hollow. That shrunk, too, so I dripped a little more on just to make sure!, Didn't want a repair with a hollow!

Here's the result:

vtsteam · « **Reply #413 on:** May 10, 2018, 09:42:21 PM »

Machining it all back down the repair was all but invisible. I'm shining a light on it at the right angle to make it visible in the photo here -- the color is slightly different, and machine marks are different, but there is no visible seam. It looks like the metal actually fused.

So we'll call this experiment a success.

awemawson · « **Reply #414 on:** May 11, 2018, 02:26:55 AM »

Excellent Steve

Good isn't it that with castings, however bad they are they can contribute to the next melt !

vtsteam · « **Reply #415 on:** May 11, 2018, 10:50:47 PM »

Thanks Andrew! Yes and this poor 5lb lot of metal was poured three times

.

BTW, here's a photo of the same repair in daylight -- it's nearly invisible.

vtsteam · « **Reply #416 on:** May 11, 2018, 11:18:43 PM »

So I dug out the spindle -- since I'm getting close to boring the headstock. I had sent for this one, standard Mini-lathe replacement, on sale from Little Machine Shop, and I must say I'm not enamored of it. Originally the idea was to save some time and machining by using a ready made, ground spindle, with morse taper , etc. But I really don't like that big hub on the end, behind the flange. It's not a bearing land, the bearing sits behind it. Therefore it adds 7/8" of overhang past the bearing.

If you add in the flange and an adapter plate to fit my chuck, we're talking 1-1/2" of overhang, not including the chuck thickness, which I think is about 4". My whole aim with this lathe was to increase stiffness wherever possible, and reduce chatter.

Another disadvantage is the loss of turning length that nearly 6" of overhanging components yields on this relatively small lathe.

So I've been thinking of cutting part way into that hub and moving the bearing closer to the flange. The only fly in that ointment is the spindle wall thickness getting too thin around the mouth of the morse taper (about 23mm ID) -- which is why I think the step is there.

So I've been thinking about increasing the journal land and bearing ID there. The original bearings for the nose of the spindle are spec'ed as 30206 rollers of 30mm ID. That gives roughly 4mm wall thickness at the bearing where it is located further back.

If I go to 35 mm journal, step up to a 30207, roller and move it forward I'll have 6mm wall thickness at the bearing, and lose 17mm of overhang. So I think that's going to be the plan.

Also, thinking about the whole flange, plus adapter plate, plus chuck thickness overhang, I'm considering eliminating the adapter plate and building the existing flange out to match the chuck's needs for register and attachment. That would probably mean brazing a ring onto the existing flange, and then turning it to suit.

In fact I've even considered extending that idea of flange improvement into a 9" faceplate, and just making a means to attach the chuck to the faceplate. I like faceplate turning -- most of my career on the Gingery lathe was faceplate turning, and I have a myriad of simple chucks and attachments for doing all kinds of work on that. I've seen people grip one chuck with another -- why not similarly grip a chuck on a faceplate?

Faceplates give the shortest overhang possible for gripping large work.

Maybe an ideal for me would be a faceplate and ER collet system, and dispense with the 3 jaw altogether. Anyway, things to think about.........

Pete. · « **Reply #417 on:** May 12, 2018, 01:35:34 AM »

That wide land is there to allow space to fit the nuts on the chuck mounting bolts.

mattinker · « **Reply #418 on:** May 12, 2018, 02:53:38 AM »

Quote from: awemawson on May 11, 2018, 02:26:55 AM

Excellent Steve

Good isn't it that with castings, however bad they are they can contribute to the next melt !

Steve,

The only draw back when re-casting the zinc alloys is zinc evaporation!

I have an Emco lathe that uses the same flange as the spindle you have. Instead of using a back plate to mount my four jaw, (a myford 7 one) I made the mounting recess directly into the chuck making things both shorter and lighter!

Regards, Matthew

vtsteam · « **Reply #419 on:** May 12, 2018, 08:30:49 AM »

That makes sense Pete. They also use a 9mm thick plastic ring/bearing cover, inset into the headstock on the Mini lathes, and part of the spindle shoulder fits into that, so the overhang isn't so apparent. But it's still there.

Since I'm building a new headstock, quite different than the Mini-lathes, bolting the chuck or other accessories won't be a clearance problem. For one thing, the bearings and spindle can be easily removed because the headstock is split, with a cap. In fact I could swap spindles, w/bearings that way for some kind of specialty situation.

But also, my headstock cap is circular in section, and my 5" chuck mounts with a much wider bolt circle, that clears the headstock cap. So I don't need to fit an allen wrench between the headstock and back of the chuck.

I've though quite a bit about the spindle this morning, and I think I'm finally going to stay with the designed bearings, and instead of reducing the shoulder, I will turn off the present chuck mounting flange and register, and continue the shoulder diameter all the way out to the face of the spindle.

Then I'll make a faceplate to fit that journal diameter. The 5" three-jaw chuck will simply bolt flat to that faceplate with three bolts. These can be easily reached outside of the headstock cap.

I'll just start the bolts, indicate the chuck true by turning and taping it into position with a wooden mallet, and then tighten. Very quick to do, in my experience with my Gingery two jaw chuck.

By turning off the spindle flange and register, and mounting the faceplate flush with the spindle end, I will have eliminated the thickness of an adapter/backing plate.

Also, when I went to measure my chuck, turns out it is only 2-1/4" thick, not 4", a pleasant surprise. So I think I've got a plan to give the shortest overhang with what I have to work with, along with a fair amount of chuck and faceplate convenience for the way I work, and I will still be using the stock bearings I have on hand. The only operation to the spindle will be turning down the mounting flange to equal the shoulder diameter.

vtsteam · « **Reply #420 on:** May 12, 2018, 08:51:35 AM »

Quote from: mattinker on May 12, 2018, 02:53:38 AM

Quote from: awemawson on May 11, 2018, 02:26:55 AM
Excellent Steve

Good isn't it that with castings, however bad they are they can contribute to the next melt !
Steve,

The only draw back when re-casting the zinc alloys is zinc evaporation!

I have an Emco lathe that uses the same flange as the spindle you have. Instead of using a back plate to mount my four jaw, (a myford 7 one) I made the mounting recess directly into the chuck making things both shorter and lighter!

Regards, Matthew

That sounds good about the chuck, Matt!

I don't think I lost any zinc by evaporation (except the figurative "evaporation": spills and such

). It wasn't liquid for more than a minute, and I never heat zinc to fuming. (Brass is another matter - hard to avoid sometimes)

In almost all casting, I pour as soon as the last solid chunk disappears in the melt as judged by a stirring rod -- I'm not a great believer in super-heating unless occasionally trying lost foam casting. Excess heat or too long in the furnace just makes for more shrinkage, and a worse surface finish.

awemawson · « **Reply #421 on:** May 12, 2018, 08:53:55 AM »

Certainly stewing aluminium longer than strictly necessary is a recipe for absorbing hydrogen and getting aero chocolate like castings.

vtsteam · « **Reply #422 on:** May 12, 2018, 09:00:58 AM »

We won't be doing that.

vtsteam · « **Reply #423 on:** May 13, 2018, 08:34:50 PM »

I used a die grinder and files on the new headstock cap. Took awhile, zinc is very tough stuff.

Most of this weekend however was spent on setting up a casting bench and organizing things under the tiny shop's attached lean-to roof. Casting will definitely be easier soon.

The shop is no longer damp after a winter with ice on the floor. The new lathe has a few spots of surface rust, though happily, not on the ways. But I decided to start painting things, maybe a few pieces of the lathe a day. So I started with the headstock and tailstock. I still need to attach the lathe's feet, so the bed painting will have to wait for that.

I'm thinking about making a boring bar and fixture for machining the headstock. I have a piece of 3/4" hot rolled steel, and a 3/4" bore cone pulley, so I think I'll use those.

vtsteam · « **Reply #424 on:** May 14, 2018, 09:29:47 PM »

Spent this evening trying to make a Ironman style oil burner for the Tiny Furnace. I have a lot of used cooking oil I'd like to burn instead of buying propane. I also want to melt brass (quite a bit higher temps than Zamak or aluminum for that matter) for the next few melts of handles and such for the lathe, so I thought I'd take the time to work up a new burner. Not much success using a makeshift version I came up with after work in the few minutes I had before dark to try it out, but I think I can make improvements to get it going properly......we'll see tomorrow.

While I have a very successful Kwiky style atomizing burner on my larger oil burning iron furnace, I'd like to do away with the compressor, as that one needs, and use a blower-only as Ironman does. But I do need to scale his down for the tiny furnace and brass, both in heat output and size.

Also today, stopped down at Lester's old time machine shop and bought some 1-1/4" hot rolled, and 1-1/8" cold rolled -- the latter for the tailstock ram.

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Author Topic: Building a New Lathe (Read 535500 times)