Lathe Bed Discussion

This page is currently just a compilation of the discussions for the Lathe Bed, spell checked and with extraneous content removed. Thanks Bruce!

How should this page be organized? Greg's first thought is to organize by bed material, then have the information that we have collected about that material organized, perhaps in pros/cons format. Following that, we could put links to external sites where info was found, and then links to the discussions in the yahoo group. Thoughts?

Lathe Bed Casting

Keith: 04/24/08

How big a machine are we talking about?

I was wondering about its size? The larger the machine is the cost of the material goes up. The weight goes up very quickly. A 6 in chuck weighs 19 lb. But an 8in chuck weighs 34 lbs. The base of the machine is the most important part of the thing. I have been kicking around fairly good size machine. The cost of the tubing is a great drawback for is construction 2x6 with a .375 wall, 60in long, are $100 each. I need 2 for the machine and they weigh 91 lbs each. With these dimension I get a machine that is good for 48 in between centers.

David G. LeVine: 04/24/08

Re: [OpenLathe] Inroduction.

There was a long (over 4,000 entries) section in the CNC Zone on epoxy-granite composites. After realizing that you need vacuum, pressure, and carefully graded fillers, I lost interest until I found that an epoxy/quartz composite was being used to repair the floor at a local Fastenal store. Holy Hand grenades, Batman, it went down easily, set overnight and worked well. The forklift didn't "eat" the floor as it did through the concrete. The aggregate was a quartz sand that had a number of different sized particles but did not need either vacuum or pressure to set up, although a thin plastic sheet and a steel plate were put over the repair so the forklift could go through to load stuff for customers. The next day the steel was off and the floor was like glass, but harder and tougher.
Concrete is not a good material because of how long it takes to stabilize and the fact that it shrinks. Non-shrinking grouts are better.

AHZ: 04/24/08

Forms? 2x6s and plywood will work fine.
How much concrete are we talking about here, lol. 4'x1'x1' is only twelve 40# bags and costs about $40. I don't know what the concrete's dimensions should be.

Cliff. Johnston wrote: 04/24/08

When it comes to selecting a lathe bed length I'd like to suggest that we keep in mind CNC conversion ability. This being the case we should design a bed length to use standard length ball screws and servos. That would eliminate the need for modifying the ball screws.

Modular is cool!

Polymer concrete/Epoxy granite/concrete:

Read the CNCZone thread on this and you will know a lot more. Basically, EG needs days to become stable and does not attack the metals, unlike concrete, which shrinks and shifts for months. EG does not need outside steel tube, but it is weaker in tension than steel, just like concrete. Many machine manufacturers use an EG base because it is stable quicker than cast iron (CI) and can be shipped sooner. EG is not "THE" answer, it is "AN" answer, and it can be a good tool.

Rexarino April 24, 2008

Alex, there are at least 2 members of this group that can build patterns for a cast iron lathe bed, probably many more than that. I'm guessing that you are in Europe. Maybe we need to identify people’s abilities and locales… If no one knows the pitfalls of polymer concrete (just an example, no slight to polymers intended) then it might be a lousy choice for material.

It occurs to me that Michael and I originally talked (and I interpreted his remarks as) about a lathe that would involve many parts built and machined by many people, each to their own ability and tooling. For instance, I can build a lathe bed pattern, have it cast, and blanchard ground locally, until my neighborhood blanchard owning machinist retires and sells his shop. I don't have facilities for line boring the headstock, so that part might be finished, or entirely built, by someone else. As parts are built and finished, with spec sheets to identify the accuracy of each, pieces could be traded around to assemble complete lathes.

Maybe this isn't the consensus of the group. Are you (ALL of you) expecting to build the entire lathe in your home shop, or do you see an exchange of parts as viable?

It certainly isn't going to be cheap to ship cast iron to South America, Europe, or Africa from the USA. Still, I think this lathe is not going to be a $500 item, rather, I envisioned a lathe that could cost up to $3000 (US), that would have the performance of an $8000 lathe.

Back to Alex's remarks: The patterns would be reasonably easy to produce, but the size (length) will have a large impact on the price of the casting. A 24” (60 cm) casting isn't too expensive, mostly governed by metal weight and number of cores. A 48” (120 cm) casting will have additional charges for the larger size.

I've read that cast iron works best if it's seasoned for some months after initial machining, so there is a lead time in months if we want cast iron.

Rexarino: 04/25/08

I can't imagine iron or aluminum castings costing less than a thousand dollars if we contract with a foundry to supply them. Beyond that, I haven't even looked at prices of basic cleanup and surfacing. It's hard to get a quote if I don't know what you want, so let's get people to vote in the polls, and we can see what we should design for.

Rexarino: 04/25/08

But perhaps a composite of various materials will work. I've been re-casting automobile wheels for a little while, and am truly astounded at the strength of a 3/8 inch thick disc of cast aluminum. If we want a lathe bed that can be built in one place, shipped to another for machining, and sent to someone else halfway across Canada, aluminum looks like a real cost saver!

I don't think I want aluminum ways, but an aluminum bed UNDER the cast iron ways - sure, I'll try that. It's an even better approach if we decide on steel ways.

And I think it's appropriate to mention that aluminum is 90 percent of the front wheel undercarriage of some SUV's, as well as the engine cradle, bumper, and various other structures. I've seen aluminum wheels that survived horrendous side impact crashes with amazingly little deformation.

I was very skeptical of aluminum when I started casting. Now I endorse it for most of the places I would have used steel. YMMV

Cliff. Johnston: 04/25/08

One of our Houston club members has a casting source in Mexico. The beds could be cast quite inexpensively there.

Alex: 04/25/08

Just want to point out that aluminum won't be a good choice. Lathe is not an airplane and is not going to the orbit.

It should turn out chips here, on the ground.

Alex: 04/25/08

But there is nothing better then cast iron to absorb shock, vibration and cutting loads. Sorry to disappoint you, folks, but I think it will be much easier and cheaper to convert a Chinese lathe to cnc then to build your own. Think about it: pouring bed, aging it, filling and painting, installing ways, lapping them, making a spindle, preloading - these kind of things can be done economically only in a factory. Plus tooling. Everything comes together for about $3K - not much, really. But by converting it to CNC instead of 3K lathe you make 30 K lathe.

Rexarino: 04/25/08

There are numerous instances of successful homemade lathes, Gingery, Model Engineer, and totally homebrew designs. So far, the polls don't show a strong desire for a CNC lathe, either. We are here to examine the possibility of using group brains and resources to achieve a reasonable product for a reasonable cost. We aren't here to convert a Chinese lathe.

I would take exception to other statements also. There are other materials that are as good as cast iron for strength. Design controls vibration, in cast iron as well as in other materials. Cutting loads - again design is as important as material.

Pouring bed? Send it to Albany, Oregon, or the Amish in the northeastern US, or to Houston to be cast in Mexico. Fill and paint? Easier than painting a Chinese lathe, and less bondo needed. Installing and lapping ways? About the same effort as making a Chinese lathe accurate. Spindle? Already available factory built, as some members have already suggested.

A Chinese $3k lathe is worth $30k with a cnc package? That may be your opinion, but it's not mine.

The people that will find this a useful endeavor are people that want to build their own, and are willing to substitute work for $$$. My gosh, homes are built by owner-builders for that reason, the Gingery list hosts numerous successful machine builders, and there are hundreds more examples of sweat-equity.

Michael Fagan: 04/25/08

The cast iron has full strength properties immediately, but it becomes more stable as it ages, so it doesn't warp. Usually you rough machine it, then season, then do the final machining once it stabilizes.

Keith: 04/26/08

I was thinking for the bed two pieces of rectangle tubing. Use channel for spacer, that could be bolted together.
Use CRS bars for the ways and screws to hold it on. 2x4 would be suitable for a smaller machine. 2x6 might be used for a larger machine. The length could be determined by the builder.
The CRS for the ways would have to be 3in wide in the top. That width will give a place for the carriage on the outside. The tailstock would fit in the middle and the over hang would be to clamp it on the bottom of the flat bar. If the CRS bar got worn out form use, it could be taken off and replaced.

David G. LeVine: 04/26/08

Alex wrote:

But there is nothing better then cast iron to absorb shock, vibration and cutting loads.

Sorry to disappoint you, folks, but I think it will be much easier and cheaper to convert a Chinese lathe to CNC then to build your own. Think about it: pouring bed, aging it, filling and painting, installing ways, lapping them, making a spindle, preloading - these kind of things can be done economically only in a factory. Plus tooling. Everything comes together for about $3K - not much, really. But by converting it to CNC instead of 3K lathe you make 30 K lathe.

Alex

Alex, while many of your points are valid, EG has been around a long time and is BETTER than cast iron for damping (see http://en.wikipedia.org/wiki/Epoxy-granite or http://www.cnczone.com/forums/showthread.php?threadid=30155 for good discussions), EG has up to 10 times the damping of good cast iron. Where it fails miserably is impact resistance, but cast iron, while better, doesn't like heavy impact either.

David G. LeVine: 04/26/08

moc.onuj|wngatorips#moc.onuj|wngatorips wrote:

hey Rex this OT for this thread but why is it mentioned about aging the cast iron? What would happen if you didn't? They make cast valves and they aren't aged at all. Just curious.

Cast iron shifts as it ages and stresses relieve themselves, machine it straight and you can wind up with a pretzel. Cast valves don't care about +/- 0.005", lathes do.

Bruce Bellows:04/27/08

The epoxy grouting (V-100) that I have used is made by Unisorb out of Jackson Michigan. I have used this product for grouting large machinery into place when leveling and alignment. It comes with the aggregate already in it. When a deep pour is required up to 8" they recommend washed crushed granite be added. They also have a product that requires no additional aggregate to be added, it’s called Deep Pour V-100 it develops a compressive strength of 14000 psi after 7 days curing. Normally Standard V-100 should only be poured up to 1”. Deep Pour V-100 can be poured up to 8". DP V-100 also has a flexural strength of 4600 psi. Some research can determine if this is a suitable product. www.unisorb.com

The cost of an epoxy product vs. a cement product. The epoxy is about 5-6 times more expensive. A 40lb bag of V-1 cement grout last cost me around $25.00. Yield was .8 cu ft. /100lbs. Epoxy grout yields 1 cu.ft. or 1728 cu. in. per kit

David G. LeVine: 04/27/08

Gene wrote:
May I ask why no aluminum? My point on mentioning airplanes and rockets is that they need strength, which can be achieved with alloy. Have you ever made a casting or a machine from Al or alloy to base your prejudice on? My next question can you make a chip now?

Simple answer: Aluminum alloys tend to damp vibrations more poorly than cast iron and aluminum, when not hard coated or at least anodized, tends to wear rather quickly.

On the other foot, Gingery did successfully design, build and have many replicas built of machines made from cast aluminum. Yes, cast iron is nicer than aluminum for many machine parts, but it seldom is as cheap or
easy to get.

Colin Johnson: 04/27/08

Hi Alex, what you are saying is generally correct about damping. The aluminum alloys are amongst the worst metals for damping, about an order poorer in damping capacity than cast iron. Steels are somewhere in between. The best high damping but rigid metals, are the manganese / copper alloys.

Damping capacity is only one property however. Many other properties need to be taken into consideration.

Such as ease of working for amateurs, wear resistance, hardness etc. Cast Iron comes out near the top. But different people have different facilities and requirements.

Gene: 04/27/08

David, my point wasn't to make all the parts from Al and did not indicated using Al for any wear surfaces. I don't know why there is so much prejudice against Al when industry has so many things made from it. If you Goggle Al alloy you will find that many have the strength of steel and machine as good as cast iron. As far as vibration damping an alloy of ZA might be better but again I doubt if there is much vibration in tailstocks, handles, carriage parts, or others that really need to be cast iron?
I made the complete Gingery series back in the 80's and agree that they are not heavy-duty machines, but haven't found anything in the size range with much more rigidity or ability. We have to look at what else has changed since Dave wrote the books - we've come along way baby!
Cast iron is a great metal to machine and it is easily cast but in the home shop is not easy to deal with. The Harbor Freight machines are cast iron but mostly junk due to poor design and poor workmanship, if a run of parts is to be made then someone would have to quality inspect and on and on!

Might just as well buy a known HD machine?

David G. LeVine: 04/27/08

Actually, I must agree, both aluminum and zinc alloys make a lot of sense for some parts. What they do not make sense for is ways and rubbing parts. The tailstock would need cast-in-place rub strips and the barrel might not last too long. Aluminum wear is still a significant problem; some of the zinc and aluminum bronzes are a whole different animal.

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