Author Topic: Building a New Lathe  (Read 160121 times)

Offline Neubert1975

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Re: Building a New Lathe
« Reply #525 on: June 25, 2018, 05:35:39 AM »
very nice casting quality.
Mine often gets porous and/or often ends up being to soft for turning in the lathe.

Offline vtsteam

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Re: Building a New Lathe
« Reply #526 on: June 25, 2018, 09:04:27 AM »
Thanks Neubert.  :beer: If too soft, it probably means you're using extrusions or other unknown scrap. Try using only aluminum castings for scrap. They have a high silicon content.

Porosity means different things to different people. Occasional very tiny bubble dots (needing magnification to see), are usually the result of dissolved gas -- often ascribed to melting in steel or iron crucibles. But many scrap castings have steel in them already (pistons for instance have internal steel reinforcing clips) or rust washed over them from outside junkyard storage, used motor oil sludge, varnish, piston rings, etc. so it's pretty much impossible to avoid ALL ferrous contamination unless you're using virgin ingot material and a non ferrous crucible. Or you can add a clay and sand liner to a steel or iron crucible. I don't usually bother doing that for my own aluminum castings, and nothing I've built has fallen apart yet. But to each his own in that department -- many internet casting discussions go back and forth repeating the same technicalities, discuss de-gassing, etc. Not many using involved methods actually build much of interest to me or detectable superior quality from what I've seen. But again, the game is the important part, not necessarily the result.

If by porosity you mean bigger bubbles and hollows, the cause is often too moist greensand, or failure to skim the melt, or some other sand contamination. Pouring too hot, is also a cause. Unless you're pouring super thin castings, or lost foam, aluminum should just be fluid, in my opinion, and not super-heated. Venting with a wire can help fill difficult cavities, though I often forget to, and usually things work out.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #527 on: June 25, 2018, 12:36:26 PM »
I've spent a good part of the morning thinking about XL timing belt profiles in order to make a cutter, and there's just no solid info on the likely tooth shape for a pulley the diameter I'm shooting for.

For making a cutter, there's the old grind it and check against an existing pulley method, more or less okay for a fly cutter, but I'm hoping to turn a profile. I do have info on the straightened belt tooth profile (rack), but that doesn't tell you what the pulley's curve will do to it.

First thoughts: straight belt profile shows a 25 degree offset from vertical for the bevel. Since I'm bending things 4 degrees per tooth in a 90 tooth circle, Maybe I should split the difference and call it a 2 degree reduction in the angle, so say 23 degrees for the pulley bevel(s).

Then  there's the width of the bottom of the tooth next. Straight line belt shows .054" there. Does it compress and shorten any? Probably. How much  on a 90 tooth circle? I don't know.

Finally I just decided to go with the plain rack proportions for the cutter -- 25 degrees, and .054" tooth end width, and .050" depth. And just file the slight tooth radii. It IS for a rubber belt after all, not solid gears. We'll try the KISS method and see how S that turns out to be.....  :loco:


« Last Edit: June 25, 2018, 01:37:35 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Building a New Lathe
« Reply #528 on: June 25, 2018, 01:06:02 PM »
John Stevenson did a treatise on cutting XL pulleys - I think his web site is still up and kept alive by his son Adam.
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Building a New Lathe
« Reply #529 on: June 25, 2018, 01:40:44 PM »
Can't find the site. Tired of research anyway, the day's a waistin'. Out to the shop......
I love it when a Plan B comes together!
Steve
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Offline Neubert1975

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Re: Building a New Lathe
« Reply #530 on: June 25, 2018, 03:31:22 PM »
Hi
Yes i have been using all sorts of scrap, but later i have mostly used alu rims from a friend of mine that have a auto repair shop.
My crusible is made of stainless steel.
Most times i have been casting stock materials in tin  cans, but i think you hit my problem with porosity (bigger bobbles) i do tend to pour quite hot, but recently i have bought my self a pyrometer, so i am hoping that it can help with the problem.
The skimming i would say is fine.

 :thumbup:

Offline tom osselton

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Re: Building a New Lathe
« Reply #531 on: June 25, 2018, 05:10:22 PM »
Thanks Tom. How is your casting going? I remember you really had a nice set up.  :beer:
Id have to dig it all out right now it is packed away in the storage shed I bought to help clear out the garage when we finished off the inside and moved the machines in. I do have a lot of aluminum and brass to melt though. The quad is blocking the entrance of course with a dead battery. :doh:

Offline vtsteam

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Re: Building a New Lathe
« Reply #532 on: June 25, 2018, 05:31:31 PM »
Hi Neubert, I don't have a pyrometer. I just watch the melt and when the pieces start to break down I give it a light stir with a 1/4" rod to feel if everything is melted and then skim and pour. For me, as soon as it's ALL liquid, it's ready. Like I said, lost foam or super thin castings might need a little more heat, say 1 minute.  :dremel:

Tom, I know the feeling exactly -- there was a delay of 2 years in this thread, when all my machining stuff was buried under other house project tools, materials, etc. Feels good to be back at it, after taking care of other necessary tasks.  :beer:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

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Re: Building a New Lathe
« Reply #533 on: June 25, 2018, 05:53:07 PM »
Well after all that blather about a multi-tooth cutter, I got impatient, and just ground a small lathe tool by hand with 25 degree angles, locked my calipers to .054", squinted as best I could at the tip, by comparison, and called it done. I installed it in the very same cast fly aluminum cutter I had bored out the headstock with, bolted down the old 5C spin indexer to the mill table, and hoped for the best.

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #534 on: June 25, 2018, 05:53:51 PM »
In action:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #535 on: June 25, 2018, 05:55:11 PM »
Finished pulley. Amazing....nothing went wrong!   :doh:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #536 on: June 25, 2018, 05:55:49 PM »
And the belt even fits.  :zap:

I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Building a New Lathe
« Reply #537 on: June 25, 2018, 06:05:25 PM »
It's ok until the phone rings as you are counting off sectors on your dividing head - ask me how I know  :ddb:
« Last Edit: June 25, 2018, 06:25:03 PM by vtsteam »
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Building a New Lathe
« Reply #538 on: June 25, 2018, 06:23:55 PM »
Andrew I don't need an excuse to do that.

Besides the 0,4,8,2,6,0 counts, this spin collet had a devilish gotcha waiting in store for the first mental lapse: the holes didn't line up exactly with the numbers -- particularly the 2 -- I nearly put the peg in the 1 hole a number of times, especially since it is the second hole, in a numbering system beginning with zero. But some little birdie somewhere above my noggin said "STOP..... not there....third hole" and I re-set the peg. A miracle this came out, first time.


HEY, and typical.....I accidentally hit modify instead of reply for your post.  Glad it was 90 tooth instead of 91!
I love it when a Plan B comes together!
Steve
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Offline Neubert1975

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Re: Building a New Lathe
« Reply #539 on: June 25, 2018, 07:13:59 PM »
Hi Neubert, I don't have a pyrometer. I just watch the melt and when the pieces start to break down I give it a light stir with a 1/4" rod to feel if everything is melted and then skim and pour. For me, as soon as it's ALL liquid, it's ready. Like I said, lost foam or super thin castings might need a little more heat, say 1 minute.  :dremel:

Tom, I know the feeling exactly -- there was a delay of 2 years in this thread, when all my machining stuff was buried under other house project tools, materials, etc. Feels good to be back at it, after taking care of other necessary tasks.  :beer:

Thanks for the advice, i will try next time casting, but first i have to fix the car steering, the belt grinder and, and and

Offline vtsteam

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Re: Building a New Lathe
« Reply #540 on: June 26, 2018, 11:44:05 AM »
Opening out the pulley bore to suit the spindle:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #541 on: June 26, 2018, 11:45:08 AM »
And finally, trial fitting the spindle, bearings and new pulley to the headstock:

I love it when a Plan B comes together!
Steve
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Offline Neubert1975

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Re: Building a New Lathe
« Reply #542 on: June 26, 2018, 12:44:24 PM »
very nice, cant be long before the first cuts  :beer:

Offline vtsteam

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Re: Building a New Lathe
« Reply #543 on: June 26, 2018, 03:52:27 PM »
Thanks Neubert. :beer:

What's going to take some time is probably sending for the right size toothed belt. Definitely not a local pickup item here. So I'm concentrating now on sizing that, which means mounting the motor.

I cut the legs of the bracket much shorter than they had been for the temporary boring bar setup at the tailstock end. Then drilled new pivot holes. Here's the motor bracket clamped for marking with a transfer punch.

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #544 on: June 26, 2018, 04:00:26 PM »
After removing the tailstock, carriage assembly and headstock, I was able to flip the bed on its side and use a hand drill to put two mounting holes in the bed. These parts are getting heavy!

Then the start of tapping. Always a little edgy putting threads full depth in 3/4" hot rolled steel. I go slow and use lots of sulphured tapping oil. Takes awhile but I do get through.

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #545 on: June 26, 2018, 04:02:44 PM »
And no broken taps, The bracket is mounted -- previously the existing treadmill motor bracket was spot brazed to a bit of pipe nipple. The whole is shot through with a 5/16" bolt. I'll add packing washers later....once I know where the pulley needs to sit.


I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #546 on: June 26, 2018, 04:07:37 PM »
The bed turned right, and other parts re-mounted to check clearances and alignments. The motor is now hinged, but resting on the bench, without a belt (or its toothed pulley -- yet to be made). I have some space for it to rise, but it can't come too far up or it will interfere with the boring table in its extreme left and back position. But there is definite room. The belt will just have to be sized right. And for that, I'll need to make its pulley.

Also I need to mill out the top of the bed's back piece so the headstock can be moved full aft before permanently mounting it.


I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #547 on: June 26, 2018, 08:49:57 PM »
Just to get a belt ordered, I kept going after dinner on this one. Rather than casting a new blank I rumaged around and went with ...

The lowly sprue:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #548 on: June 26, 2018, 08:55:46 PM »
Turning down to 1.126" for a 18T XL driver:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #549 on: June 26, 2018, 09:02:33 PM »
I turned the ends down to .875", bored .667", and since the old setup was still in place on the mill, all I had to adjust was the depth of cut, after tightening in the collet. The tooth cutting was much easier, only 18 teeth, and no need for the vernier -- just rotate to every even hole.

I love it when a Plan B comes together!
Steve
www.sredmond.com