Building a bed turret

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John Hasler
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Re: Building a bed turret

Post by John Hasler »

Did you shim the part?
RSG
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Re: Building a bed turret

Post by RSG »

John Hasler wrote: Sun Dec 06, 2020 11:36 am Did you shim the part?
Since I did a pre-finish on the surface with the parts in the vise I didn't feel the need to! When I place the part on the table they don't rock. I'm just concerned that with the amount of compression under the clamps that it could distort the blocks by a few thou. when moving the clamps to the other side.
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GlennW
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Re: Building a bed turret

Post by GlennW »

After seeing what you are doing, I'm not sure that you have the table capacity to do exactly what I had in mind.

I was thinking to clamp more toward the center as shown in Post #12 on page 2. That along with blocking the part as you have done on the one side would keep it from moving around so that you would need very little clamping pressure to secure the part. That would lessen the chances considerably of deforming it due to clamping pressure. That would seem be far better than just clamping on the two corners.
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RSG
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Re: Building a bed turret

Post by RSG »

GlennW wrote: Sun Dec 06, 2020 12:54 pm After seeing what you are doing, I'm not sure that you have the table capacity to do exactly what I had in mind.
So would I be better off using the vise to so the final surface finish to square that face up then?
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John Hasler
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Re: Building a bed turret

Post by John Hasler »

GlennW wrote: Sun Dec 06, 2020 12:54 pm After seeing what you are doing, I'm not sure that you have the table capacity to do exactly what I had in mind.

I was thinking to clamp more toward the center as shown in Post #12 on page 2. That along with blocking the part as you have done on the one side would keep it from moving around so that you would need very little clamping pressure to secure the part. That would lessen the chances considerably of deforming it due to clamping pressure. That would seem be far better than just clamping on the two corners.
I'd also block it all the way around and put shims under the part directly below each clamp.
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Harold_V
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Re: Building a bed turret

Post by Harold_V »

RSG wrote: Sun Dec 06, 2020 12:04 pm
John Hasler wrote: Sun Dec 06, 2020 11:36 am Did you shim the part?
Since I did a pre-finish on the surface with the parts in the vise I didn't feel the need to! When I place the part on the table they don't rock. I'm just concerned that with the amount of compression under the clamps that it could distort the blocks by a few thou. when moving the clamps to the other side.
The idea of distorting because of clamping pressure is not realistic. Compression strength of gray iron is exceedingly high, although it is rarely good in tension (depends on the given alloy). When tension strength is desired, the choice should be ductile iron, not gray iron.

So long as the part is fully supported beneath the clamp, and the base is already in full contact with the table, distortion won't happen. The only time a shim would be required is when the above condition is not met. Shims are not used to straighten a part, they're used to prevent distortion. Said another way, they are used to prevent a part from shifting from its natural state when a clamp is applied. Already flat? No need (nor place) for a shim.

One thing to consider. When you're working to less than three thou, it's not common for the human eye to be able to discern that small amount of movement. When checking for movement, an indicator is recommended. Alternately, one can use a thin feeler. With an indicator in contact, you can observe any movement when a clamp is applied. If there's movement, the part is not flat. You are highly unlikely to be able to apply enough pressure with table clamps to compress gray iron, assuming you don't have them applied such that they are bearing only on a tiny edge of the clamp. Keep them parallel to the top surface and they can't indent the part.

H
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RSG
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Re: Building a bed turret

Post by RSG »

Thanks for the input fellas. I went ahead with machining the two long slender sides today clamping them to a 4.5" angle block and am happy with the results. They are square within a few thou and the same for finished size. At first I thought I needed to send them out to be ground but as Harold mentioned if the parts don't require it then there's no sense. Looking at the drawings I can't see a reason why I need to.

Anyway I appreciate the help so far, I'll have more questions especially when it comes to drilling and tapping some holes in one end of the 12" block. Fixturing that upright in the mill might be a rigidity challenge.
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Harold_V
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Re: Building a bed turret

Post by Harold_V »

I hope I didn't instill a false notion in your thinking. Grinding will almost always improve surfaces. Grinders are simply higher precision machines. The question then becomes the one of is it necessary? If you're trying to establish a fit whereby you have two rigid members and one must move within the other, and there is metal to metal contact (no spring pressure, for example), then grinding is most likely to improve the fit. That's due to the ways of grinders being more precise, plus a grinding wheel will leave a better surface, with much smaller irregularities. Those irregular highs that are common to milled surfaces may introduce spots where movement is restricted, adjacent to spots where it's loose. That's why precision surfaces are either ground, or scraped (which offers an even higher degree of precision).

You most likely would benefit by grinding. All depends on the nature of the cuts you can achieve with a mill. Just keep in mind, it is a mill, not a grinder. Key to success here is if you are happy with the results you achieve. I'd like to say that it's not a matter of right or wrong, although grinding has the potential to yield better results.

H
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pete
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Re: Building a bed turret

Post by pete »

I'm trying to visualize how these plates are going to be used RSG. Are they to form a hollow box for that turret? If so then leaving them very slightly over size and doing your finish machining after assembly would get you the best accuracy your mill can provide and the most accurate finished part. With a bed mounted turret then traversing with the lathe carriage and an indicator onto the turret assembly in it's working position would show any deviation for your exact alignment and elevation. Final fitting to the lathe bed could be done with a light coat of scraping blue on the lathe ways and hand scraping for that exact alignment. But all this is worthless if that's not how there being used.
RSG
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Re: Building a bed turret

Post by RSG »

Good idea with the bluing Pete! I hadn't thought of that for fitting the saddle base to the lathe bed. As far as accuracy is concerned, I feel that it isn't as necessary as one might think, there are gibs to be made for the slides and a few other adjustable capabilities built in to the design. In the end the turret tool holes will be bored using the lathe itself so the exact position will be correct.
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pete
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Re: Building a bed turret

Post by pete »

Yep the holes will be correct. But only if the turret slide is exactly parallel with the lathe bed ways. If the slide has any misalignment up,down,left,right those holes will only be on the head stocks C/L at the position of the tool slide they were bored at. And if there bored and you later try to correct that alignment it will be a more than a complex 3D puzzle to get the correct alignment as well as keep all the holes at the correct elevation.It would be much easier to hand scrape for the correct bed way fit, then indicate for a check, and then finish machine the turret's way's true to the then known to be correct way surfaces on the turret's base. Once that's complete you can then drill & bore the station holes in the turret.
RSG
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Re: Building a bed turret

Post by RSG »

Finally gotten around to finishing the machining of the cast iron components for the bed turret! This is the absolute worst material to work with bar none! Harold was right, it literally gets in every nook and cranny of your shop! The stuff is so dirty its disgusting! I taped off my anodizing room with plastic and when I went in the other day to get some gloves the box that sits on the top shelf was covered in black soot, how? How does it migrate so well. Good thing I wore a respirator with machining. Every time I came in the house my wife said I looked like a coal miner with my black face. I am now in the process of stripping every tool, every container, every surface of the shop and washing them all down with soapy water. The bucket goes black within a few minutes.

I can say this with some certainty - I will not be machining ductile iron again! Anyway here's what I got so far.

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Thanks for looking
Vision is not seeing things as they are, but as they will be.
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