Setting the compound at 0* or 30*

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RSG
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Re: Setting the compound at 0* or 30*

Post by RSG » Tue Jan 08, 2019 9:44 am

Thanks for the added info guys!

Harold - While I won't argue with what you regarding rigidity when the tool post overhangs the top slide, I have to wonder how important it is when turning aluminum. Perhaps yes? maybe not? Either way loosening and tightening the gib constantly wont work well for me as I do a lot of angle cuts on my parts, sometimes as many as six in one part, then repeat that several times for the entire project. I think your advise will be taken into consideration when I turn steel components though unless I make one of those fancy tool post holders as Robrenze has.

Pete - once again you have given us information that, whether you realize it or not is invaluable! (Robrenze). After watching some of his videos
(particularly the one on his tool post mod) it has inspired me to try to make one for those times I am working with steel.

So, for now - what I have taken away from the topic is turning the compound to 30* can help with rigidity since it brings the whole mass closer to the cross slide. Is there anything else I can do to make my current set up more rigid?

Thanks
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tornitore45
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Re: Setting the compound at 0* or 30*

Post by tornitore45 » Tue Jan 08, 2019 10:01 am

Since I have acquired a test dial indicator that reads 0.0005" I have come to appreciate elasticity and the fact that Young modulus is not infinite has it appears to from daily experience.
Finger pressure onto beefy structures result in appreciable deflection. Every piece of the machine that appear "Rock Solid" can be flexed by hand. Imagine what biting down on a cutting edge can do.
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liveaboard
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Re: Setting the compound at 0* or 30*

Post by liveaboard » Tue Jan 08, 2019 1:02 pm

Harold_V wrote:
Mon Jan 07, 2019 4:28 pm
It's dead easy to build a bracket to hold a long travel indicator. While my Graziano has a calibrated dial on the carriage feed, I still use such a setup. It's far more reliable, and lightning fast to adjust to the desired location. My setup allows for the use of longer than 1" travel indicators, too. I recommend it highly, especially if you face multiple lengths of cuts that demand precision. By recording positions once established, you can do multiple parts in far better time.

H
Thanks; it's one of those things I'd like to do.
There are just so MANY of those things...

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Re: Setting the compound at 0* or 30*

Post by pete » Tue Jan 08, 2019 5:02 pm

RSG, Robin is one extremely talented and clever guy. Any video he's done is well worth the time.

Tornitore45's point about seemingly rigid machine parts having higher deflection rates than you'd think is the main reason I now don't even have a drill press for metal working. Any drill press I can afford and my shops floor can handle the weight of is simply built far too lightly to be worth while. My 250 lb floor model Craftsman seemed ok until I put an indicator on the table edge and applied maybe 15 lbs of thumb pressure. Seeing .030" + deflection was enough for me. I've read it takes approximately 150 lbs of drill point pressure just to drill a 1/2" hole in mild steel. Varying work piece weights make it pointless to try and adjust the table with any hope of compensating for that deflection. If I had a concrete floor I'd probably try and find a smaller radial type. Instead I just use the mill.

Something to maybe consider RSG. George Thomas detailed in his book The Model Engineer's Workshop Manual about why the gib screws on set screw adjustable gibs were a very poor working design. Most of them have tapered points that are supposed to engage and from past experience wear slowly further into divots in the gib. His diagram explaining what happens as the slide gets moved was again something I'd not considered. With the minute but critical clearances any slide has to have then as the slide moves the gib tries to ride up the slope of those pointed screws resulting in a further tightening of the gib due to that wedge effect. What he did was drill a small hole through the side of the cross slide and just through the gib while it was in it's working position with all the parts clamped in place using the adjusting screws. Pulled everything apart, deburred and then reamed the hole in only the side of the slide. Reassembled and then inserted a shop made pin.

In use the pin has minimal slip fit clearance on the slides casting and a light press fit on the gib. That keeps the gib from making that very slight longitudinal movement. Not mentioned by him, but I think the light press fit was simply to keep the pin from ever falling out. He also added a small shop built threaded gib lock with a short pin lever to the top slide as well. It was a fairly lengthy article and much too long to repeat it all here. But his opinion was that most keep there slides much too tight. In that condition very small movements are impossible until the screw is moved enough to overcome the tension between the parts. That results in a stick/slip situation. He advocated adjusting slides without the screw being attached because hand moving the slide allows you to feel when the adjustments are either too loose or too tight. Since reading his points that's how I now adjust mine when it's possible. If you really wanted to get picky then using an indicator at different areas on the side of the slide would allow checking any loose condition. Because there has to be "some" clearance to allow the slide to even move and for oil, absolute perfection would be just about impossible. But getting the correct average adjustment of not too tight or loose takes a pretty good feel to do it well. Not having the screw engaged makes that feel a whole lot easier. Tapered gibs are a much better design in my opinion since the gib is restrained from moving end to end. Adding a small gib lock solves the issue of having to reset any adjusting screws that were carefully adjusted. On a highly worn lathe then getting really fine adjustments on the gib probably isn't going to work that well. I still think pinning the gib strip on non tapered gibs would be worth it on a lathe that uses the set screw design. And from my limited experience the less you pay for a machine then the more you need to go over and check what you've bought. Bent or I guess banana curved gibs would be the better description right from the factory isn't all that uncommon with some of the off shore machines. :-(

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BadDog
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Re: Setting the compound at 0* or 30*

Post by BadDog » Tue Jan 08, 2019 5:19 pm

Regarding locking the gibs, my lathe compound has a slide lock with toggle so that the slide can be locked and unlocked with trivial ease without having to worry about general sliding (re)adjustment. Mine is a fitted tapered gib, but I see no reason you couldn't add one (or more) lock tool-free screws between the adjustment screws for the same benefit. This is also how most boring heads work. You never touch the gib adjustment, but rather use a different screw to lock the slide.
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Re: Setting the compound at 0* or 30*

Post by Harold_V » Tue Jan 08, 2019 5:53 pm

RSG wrote:
Tue Jan 08, 2019 9:44 am
Thanks for the added info guys!

Harold - While I won't argue with what you regarding rigidity when the tool post overhangs the top slide, I have to wonder how important it is when turning aluminum. Perhaps yes? maybe not?
Not nearly as important as it would be for a guy turning tough materials. That's why I said "From my perspective, yes, using your lathe as you suggested is not in your best interest. It most likely isn't much of a problem for you, however, as you're not really loading your machine because of the nature of your work."

Aluminum simply doesn't create the same problems tough materials create. Should you ever decide to machine steel, even mild steel, you'd see the difference by following the advice that has been provided. Mean time, if what you do works for you, no need to change. :wink:

H
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Re: Setting the compound at 0* or 30*

Post by Harold_V » Tue Jan 08, 2019 6:08 pm

tornitore45 wrote:
Tue Jan 08, 2019 10:01 am
Since I have acquired a test dial indicator that reads 0.0005" I have come to appreciate elasticity and the fact that Young modulus is not infinite has it appears to from daily experience.
Finger pressure onto beefy structures result in appreciable deflection. Every piece of the machine that appear "Rock Solid" can be flexed by hand. Imagine what biting down on a cutting edge can do.
Absolutely true! It's particularly noticeable when you have a machine that has adequate horsepower but isn't necessarily the most robust of machines. I'd like to use my Graziano Sag12 as an example. It is powered by a 3 horse motor. The machine is capable of taking respectable cuts, such as .200" off (per side) with coarse feed. To do that, I use negative rake carbide. When the cut begins, if one pays attention, there's considerable movement in the carriage assembly. The tool post dips a little, and the entire assembly appears to "squat" under the pressure of the cut.

When I worked in precision grinding, one of the items that we ground in huge abundance were the bearing housings for the guidance system. We had a one way tolerance of .0002" on the bores, where the bearings were installed. The machine (Heald model 252 internal grinder) had a pick feed capable of taking a tenth at a time, but it wasn't uncommon to find the bore within a few millionths of size, but taking a tenth wasn't necessarily desirable. In such a case, one would red the bore (using a wax pencil), then start the machine. Allowing the wheel to "spark" the bore until it was stable, there would be a uniform covering of red. A finger, lightly placed on the wheel head, would remove the red color, albeit slowly. When it was gone, you were pretty much assured that you had altered the bore by about .000020", usually sizing the bore within tolerance. Speaks volumes about the flexibility of machine tools, even when they are quite robust, as the Heald was.

When operating precision grinders, one learns to NEVER touch the table or wheel head while it is in operation.

H
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Re: Setting the compound at 0* or 30*

Post by RSG » Fri Jan 11, 2019 1:15 pm

Good advice once again, Harold, I learned about the "touch" thing you speak of on my old mill. If you rested your arm on the side it would alter the measurement. I'd like to think my new mill is more robust and could mitigate this but I expect it to still happen.

BadDog, Thanks for the idea. I'll have to look into that. I was at my friends shop and he has a 14-40 Clausing/Colchester and the tool post and top slide both lock.

Pete, thanks for the detailed info regarding the gibs.
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liveaboard
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Re: Setting the compound at 0* or 30*

Post by liveaboard » Sat Jan 12, 2019 2:47 am

The first power miter saw I bought couldn't cut a straight line in heavy stock; fitting floorboards was a disaster.
The rods would just bend from the load during cutting.
Better ones came out [expensive], so I used to just grab the thing in the shop and see if it would deflect with a little arm pressure; they all do, so I never replaced my horrible first machine.
After reading this thread, I realized my test is far too severe.
Still, even the 1,000 euro Festool flexes several mm with a slight push.

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Re: Setting the compound at 0* or 30*

Post by spro » Sat Jan 12, 2019 3:56 am

I think this goes back to alignment or static tramming. The machines flex under pressure but there is a point where the tooling pulls. I have to remember this because the shims and bolts through the column flange make a difference. My old mill/drill was set up so awkward with its shims, I corrected it. I found that static alignment was not the same as under pressure. Milling isn't , especially with the quill locked, the same as drilling.

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