Shoring up my 618

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veniceboo

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Understanding that the Atlas 618 is a small lathe, almost a toy even, I'm wondering if my OEM legs and the motor mount are adding to the vibration and if there's anything I can do that would tighten the lathe up. The reason I think the legs are part of the problem is that the footprint is not very big, and even though the lathe is bolted to the concrete floor of my garage you can only do so much downward.

Then there's the way that the motor is mounted, which I assume is the way these came from Atlas? I'm very new to machining and until I got this lathe I had never turned anything on any lathe whatsoever. I know that pictures are not enough to diagnose the problem but I am suspicious that the motor arrangement is part of the problem and the lack of base width is keeping the lathe from being more stable even though it's bolted down. Thoughts?
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I don't have a 618. I have a Craftsman 12x36. So what I have to say may not be applicable to your lathe.

Have you looked in the MOLO (manual of lathe operations) for info on how the lathe should be mounted. You should make the small donation to the forum so you can access the downloads section. A copy of the MOLO will be in the downloads. This would be the first thing that I would do.

The first thing that I noticed in the pictures is the wood bench top has a split in it. This could be part of the problem. Is the motor held firmly in place? Or is it allow to float with only the weight of the motor keeping the belt tight? My 12x36 has a screw that keeps the motor from moving and keeps the tension on the belt.

Have you checked the lathe bed for twist?

Have you checked all bolts to make sure they are tight.

These would be the things that I would check first.
 
Thanks for the tips. I have a brand new, shiny copy of the MOLO and I will dive in. I didn't know about donations and I went and did that as well.

As I look at the pictures I feel like the motor has sparse bottom support. It's tight to the leg assembly but I think a big culprit is how there's so much mass hanging off the side.

I'm in the early stages of trouble shooting this and the lathe runs well enough for what I'm doing with it right now, but I'm going to want it to be more accurate in the near future for more advanced things.
 
I sold my 618 recently but I think your motor mount looks unmolested.

What do you mean by "vibration"? Do you mean that the surface finish is poor with a wavy pattern? And the lathe vibrates and makes noise while taking a cut? AKA "chatter"?

Getting the spindle preload right is critical for achieving good finishes with the 618. Also the gibs need to be adjusted so you can move the related controls but there is as little play as possible. If your 618 has significant wear, by the time you get the gibs tight enough in the worn spots, it will totally bind up in the less-worn areas.

BTW, IMHO, high speed steel cutters are infinitely superior to carbide on the 618. A really sharp HSS cutter with appropriate rake angles will peel metal off and leave a very good finish.

Craig
 
Hi guys, I should have been more clear. I know that there are any number of factors that affect surface finish and I need to address some of those and others I have already. I was just growing curious about the amount of vibration that I feel when the lathe is running, and it occurred to me that no matter how much I level it and align it I will be fighting that. On some level it's a lightweight machine so there's no ballast to it to keep it from vibrating. I just looked at the motor arrangement hanging off the back like that and I see it as a candidate.

As sexy as those Atlas legs are, my possible solution would be to ditch them and put the lathe on a very heavy wooden bench with a wider base, that is also anchored laterally to the studs in my garage. I'd mount the motor to the bench behind the lathe so that it's supported. Most of the 618's that I've seen- like Jster1963 (sp) on Youtube, seem to run much smoother and quieter than mine and they don't look like they are vibrating. The vibration on mine is not bad, I'm just seeing that it might be something that needs to be addressed. Maybe what I should do is address the alignment issues and leveling issues completely and then see if my surface finish is suspect.

On another topic, related to WCraig's mention of HSS cutters, where do you get quality ones that are already ground? All I see and have are carbide brazed as well as indexable cutters. I'm far from being able to grind my own cutters at this point as I'm a real newbie. Thanks for all your help.
 
Little Machine Shop has some pre ground HSS lathe cutter sets.
 
Just a suggestion, take the drive belt off the motor, start the motor. Do you get vibration? Yes, then balanace or replace the motor. No? put that belt back and take the next one off. Try that? no vibration? are the belts good and snug but not stretchy tight? are they flopping? Oh that's right, you've got segmented belts. Well, at least you know the vibraton is or isn't coming from the drive...
 
I got alot of vibration on my 618 from having the motor>countershaft belt tensioned by motor weight alone. The motor would "climb" up the belt and then fall back, essentially bouncing on the belt. A positive stop to the motor movement, so the motor belt was tensioned against that stop, got rid of alot of the vibration. The rest went away with a balanced treadmill motor, a poly-V balanced countershaft pulley and a DIY spindle poly-V pulley. The last one was mostly to improve belt grip so a cut didn't stall the spindle all the time. Bolting to beefier stand or bench won't do anything for vibration (or relatively little), but it will allow you to take bigger cuts up to the limits of the carriage/ cross-slide.

As others have said, regular molded carbide inserts (eg. CCMT) won't work well on this lathe, but the ground ones for aluminum (eg. CCGT) work exceptionally well, better than ground HSS. Not to say that you shouldn't learn to grind HSS, as that skill will come in very handy, but you can take an initial short cut and get yourself some SCLCR turning/ boring tools and a pack of CCGT inserts.
 
Thanks to everyone for the replies. That thread Mikey started about grinding HSS tools is gold. I think my motor or the drive belt is the culprit so I need to trouble shoot that.
 
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