Have a problem with QCTP and Grizzly mini-lathe

[grimm]

I have the same lathe as you and I just removed the detent. Mine wasn't held in with anything and I just pulled it and the spring out. Even with it in place and using the original tool holder I found that it got in the way more often than it helped. To get the QCTP aligned, like for parting, I just use a square.

[John Evans]

Or a 1-2-3 block on the chuck face to side of TP. Lots of ways to skin that cat! LOL

[pete]

I'll second Harold's advise. I can say it will be only a matter of time before you have an endmill pull out of that drill chuck and either ruin your workpiece, or if your edge milling with the side of the endmill, the endmills helix will do a great job of pulling it right out of that drill chuck. Then you have a razor sharp endmill spinning at whatever rpm you had the machine set at, and bouncing in all directions. Collets or endmill holders are the only safe way for the average HSM to hold an endmill.

I'll give you a couple of examples about just the ER 32 and 40 series of collets. The recommended torque requirements to hold an endmill in these collets which surround the endmills shank, and hold a far longer section of the shank than any drill chuck can are approximately 100 ft. pounds for the ER-32's and 120 ft. pounds for the ER-40's. I highly doubt a small chuck key would give you even 30 ft. pounds of closing force and that's with only 3 tiny chuck jaws doing the gripping.

There is NO drill chuck made that's safe to mill with. Yes there's multiple fools on Youtube that try and say a drill press and drill chuck will work, IT DOESN'T AND IT CAN'T. In fact it's just about impossible when you compare what's needed in a drill presses design to even a cheap mill. And while a milling attachment used on a lathe doesn't work all that well, I can assure you there light years ahead of any light weight home shop grade drill press. Your chuck may screw on, that doesn't solve the problem that it's extremely doubtful your drill press has anything more than the usual drill press type of bearings. Those aren't designed to work with the side forces that are common with milling. Even 3 jaw lathe chucks that have a hell of a lot more closing force aren't recommended as a way to hold endmills as they still can't usually hold an endmill tight enough.

Pete

[sts_66]

I have the same lathe as you and I just removed the detent. Mine wasn't held in with anything and I just pulled it and the spring out. Even with it in place and using the original tool holder I found that it got in the way more often than it helped. To get the QCTP aligned, like for parting, I just use a square.

I did exactly that last night, thought I got it lined up perfectly, then started turning down my work piece - measured the diameter ~ 20 thousandths later and found (again!) that the rod had a slight taper - was 0.466 at one end, 0.462 at the other - part is only 2" long!? Rechecked the tool post, found it had twisted, was no longer square. Tried realigning it, but every time I went for the final torque down it twisted a bit (tried to use more torque than I had previously) - I assume that's what the stock pawl was designed to prevent. Gave up for the night.

This morning was thinking about it in bed, and realized that the "squareness" of the QCTP is irrelevant to getting a straight cut along the rod - only a couple things could cause a taper:

1. Dead center in tailstock is off-center: Was off a few mils from the factory, corrected it, have swapped drill chucks and the dead center multiple times since then, it might be off again - not likely, but possible.

2. Run-out of the lathe chuck is sloppy: not likely - I turned down several pieces that were straight to < 1 mil after resetting the tailstock

3. Dead center is pushing on the nylon rod too hard and warping it while turning - possible, but visually I don't see the rod wobbling along the length, dial indicator says the rod is round, just not the same diameter along the length.

4. I'm taking off too much material per pass, causing the rod to warp from the load - "only" taking off 4-5 mils/pass, same way I made the prior good parts of same length, but maybe I got lucky - used the stock turret to make those. Really have no clue what the max turn down per pass is for such a soft material that can easily warp under load.

I just got a live center, so I'm going to part off the dead center end of the rod to get a clean straight surface, replace the dead center with the live one, recheck that it's on center, then try again.

[SteveHGraham]

The problem is re-aligning the QCTP to be 100% square to the lathe axis after rotating it (or removing it) - that's what the pawl and scallops on the bottom of the stock turret do.

Most important thing to note: it looks like you're trying to do something you don't need to do.

Unless you're parting, you probably will not need to align the post with the work, but just so you'll know, you can align it by loosening it and moving the carriage so the post presses against a known square surface, such as the chuck jaws. If that's not precise enough, you could put an indicator on the headstock and move the tool post in the x direction, turning it until you get no dial movement. It will do nothing to align the tool with the work, though, unless it's a parting tool, and even then, you could probably do better measuring off the tool and not the holder.

When your old turret post was in use, with the pawl, it may or may not have been completely square to the work face, and even if it was, the tools held it in usually were not. When you put a cutting tool in a turret post, you generally don't align the tool precisely. You just stick it in there and tighten the set screws. If you're cutting threads, you use a fish to align the tool. The position of the tool post holder doesn't matter at all. You can have a tool which is 5 degrees off from the holder's position.

The orientation of the tool won't cause you to cut tapers. The tool tip will always move in a straight line, because it is constrained by the carriage and ways. If you're cutting tapers, something is out of alignment. Maybe the headstock needs to be trued up. On big lathes, the beds have to be lined up using levels and so on. I have never heard of anyone doing this with a 7" lathe, though. They're short, and they come mounted on rubber feet.

If your tool is not held in tightly, it could shift, resulting in a taper. The workpiece would probably get wider as the tool moved along, because the tip would move away from the work. I guess it could get narrower if the tool dug in. The post has to be tight, and so do the set screws.

If you need to know where the tip of the tool is in relation to the work, you can use rolling papers or cellophane.

[sts_66]

If your tool is not held in tightly, it could shift, resulting in a taper. The workpiece would probably get wider as the tool moved along, because the tip would move away from the work. I guess it could get narrower if the tool dug in. The post has to be tight, and so do the set screws.

I think that's what happened - on one of the first passes, at the end of the rod supported by the dead center, the cutting tool started chattering, roughed up the surface instead of cutting it - I think the tiny hole created by the dead center on the end of the rod got enlarged as well. Tightened up the screws holding the tool and the chattering stopped, but think the damage had already been done - when the tool got near the dead center on further passes, the rod probably wobbled slightly in the enlarged dead center hole, causing the taper. This wouldn't happen with a metal rod, but with soft nylon the dead center drills a tiny hole in the piece, no way to prevent it - live center should resolve that problem.

[SteveHGraham]

My advice is to bug Harold and Richard. They know everything.

[John Evans]

You are using a 'center' drill to create the hole for the center to run in aren't you? From what you write it sounds like you are just forcing the dead center into the work. You are using a HSS dead sharp tool I hope.

[sts_66]

1. You are using a 'center' drill to create the hole for the center to run in aren't you? 2. From what you write it sounds like you are just forcing the dead center into the work. 3. You are using a HSS dead sharp tool I hope.

1. No - never did that back when I was machining metal rods in my youth, and the lathe manual says nothing about doing that, just recommends lubing the tip of the dead center while turning.

2. Yes - applying enough pressure to support the rod by not enough to "drill" a biggish hole in the end - it's an extremely tiny dot.

3. Yes, standard 60 degree taper.

Back to #1 - had considered doing that, wasn't sure the center drills I have had 60 degree tapers, but it appears they do:

http://www.harborfreight.com/center-dri ... 60381.html

New live center has same taper - are you suggesting I countersink the end of the rod first to better support it, regardless of which center I use in the tailstock? I guess that would help prevent the loose tool chattering problem if it occurs again?

[SteveHGraham]

I have a fantastic idea. Go to Swarfrat.com and invest in their mini-lathe videos. Alternatively, you can rent them from Smartflix.com.

You will want to look beyond the lathe manual.

Youtube is full of good stuff, too.

[sts_66]

I have a fantastic idea. Go to Swarfrat.com and invest in their mini-lathe videos. Alternatively, you can rent them from Smartflix.com.

Nah, more fun to make mistakes then figure out how to solve them, LOL. Except when using power tools that turn at 8,000 - 10,000 rpm, of course. Radial arm saw is used only as a last resort if the table or miter saw can't do what I need done - as a 4 yr old, witnessed my Dad accidentally slice one of his fingers in half while using it, split right down the middle to the second knuckle (same saw I now have) - put the fear of god in me permanently!

[John Evans]

Yes you need to center drill before using a center live or dead. May i suggest you aquire either the Atlas/Craftsman or the SB book on how to operate a lathe . The advice there may be a bit dated but it will be correct unlike some Youtube info.
PS please update your profile so it shows at least your general location on your posts.City-State if fine.
PPS Your mini lathe can do a lot of damage to your person even as small AS IT IS !