Plans for a Levin-like Steady Rest…

@david pierce wrote:

Tom,
The drawing is excellant and very professional looking. When drawing a mechanical part it is good to keep in mind that everything in the drawing has to be made by a machinist with their available tools. For example, if a piece of 1/4″ crs has a square hole in the middle, it is less expensive and time consuming to require that the hole has rounded corners if the square hole is to be milled. Square ID corners are easier to draw but more time consuming to machine. With outside corners the opposite is true. Square outside corners are less time consuming than rounded outside corners. Tight tolerances are also expensive. If a drilled hole is good enough to make the part function properly then it should not be toleranced to .0001 inches. Different tolerances require different machining processes in order to produce a part.

Thanks david. When we did contract design documnts we always listened to those who did the work in the field as sometimes they could do something better and cheaper than what the engineer of record had specified in the design. So… I do understand that I have a lot to learn. Yet, this kind of commentary is super helpful for me and I really appreciate it. I’ll try to remember all of these points as I go.

@david pierce wrote:

If you get the HF mill and begin to make the part that you drew, you will begin to rethink the design. You will ask yourself: How do I make this angle? Do I machine it out of a solid block of material? Do I take a piece of flat stock and bend it? Do I fabricate it from two pieces of flat stock? All of these issues affect the cost of the part. The only way I know to get a feel for this is to jump in with both feet and cut some metal.
david

I thought about if I had that HF mill, how I could mill the bottom of that plate – or, how would I make the angled edges that fit on top of the lathe bed bar.

Regarding the grade of steel… is what I have shown even in the ball park? If you were making this part, what grade of steel would you use?
I really appreciate every you post.

Thanks,
tmac

@david pierce wrote:

Tmac,
If it was me I would reduce it to the simplest and easiest way to manufacture the part that I knew how to do. The bottom of the device shows the tapers of the lathe bed machined into it. This would rule out cold rolled steel as it warps when machined this way. Is it necessary for the unit to lock into the bed with a precision fit the same way as a tailstock that would slide along the ways? A tailstock has to have a precision fit because there is no way to adjust anything. A steady rest has adjustable jaws meaning that aspect of the part is not necessary; so a flat plate would also work. The jaws resemble milling machine clamps. Do they require the size and strength that are specified in the design or could the same functionality be accomplished with brass set screws? Drilling and taping three holes for set screws if far less expensive than machining three slotted jaws and the slots they ride in.Also, three brass set screws will be at least as, if not more precise than, the sliding jaws. Steel is more difficult to machine than aluminum so does the part require the strength of steel or will aluminum accomplish the requirements for the loads that will be put on it? In short If it was me, I would reduce the design to the minimum cost and effort that would do the job properly.
david

david:

That’s one of my main problems. Never having worked in a machining environment, I am ignorant of the loads placed upon such a tool on a small lathe like the Levin – and manufacturing practices. So…It sounds as though, aluminum might work in this instance. I guess I can just jump in and if it fails – it fails. It sounds like I need to back-up and re-think the design.

Synopsis:
1) Lose the slotted inteface and just go with a flat bearing surface.
2) Use aluminiunum
3) Employ a different holding scheme (perhaps use the rod system posted previously by William)

Before I begin, can you give me a good guess (for this application) on the thickness and grade of aluminum for this?

Thanks!
tmac

@david pierce wrote:

Tom,
6061 aluminum is a good material to machine and is not horribly expensive like 2024. A 1/4 x 2 x 72 inch bar is about $30.00 and a 1 inch diameter bar of round stock is about $10.00 from MSC. There are many metal suppliers that are much cheaper than MSC but you have to hunt for them in your area. The three rod supports can be made from a length of 8-32 brass threaded rod that can also be purchased from a metal supplier or hardware store. Keep in mind that the largest diameter rod that is going to be supported and machined will probably not exceed 1/8 of an inch so design the hole to clear that (3/16-1/4). There is no need to have the front open as this is a steady rest not a follower rest. If you machine the front open it will require extra work and weaken the part. The rod supports can be located at 90 degrees, 210 degrees and 330 degrees. Since the bottom will be clear (270 degrees) a hole can be drilled and a round shaft inserted and secured with Loctite. The other end of the round shaft can be inserted into the base and also attached with Loctite. The loads on this will be extremely light due to the small size of the parts that will be machined on a WW lathe.
david

david:

This gives something to think about.

Thanks!
tmac

All.

Ok… I’ve given this some more thought (oh oh) and it would seem that I might need two of these – one like William’s design for clock repair and one for watch repair. Since William’s is already pretty cool and does the job, I’ll concentrate on the watch repair version.

Later,
tmac