Turning parts with features on reverse

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lsteele
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Turning parts with features on reverse

Post by lsteele » Fri 26 May , 2017 10:11 am

Hello,

I'm trying to work out the best (or any) approach to tackling parts which can't be turned from one end only. I'm used to manual turning on machines where I had collet and 4-jaw chucks, so if I needed to machine from the other side I could take the part out and remount with confidence of concentricity. On the Orac that's not an option, or I'm confined to the best concentricity I can get with the 3-jaw.

I wondered about using a left-hand tool for features like flanges, but that requires having stock extend further out from the chuck. I also recently saw some videos of grooving tools being used for profiling. Now I had always understood a grooving tool was for grooving only, but I bought a cheapo (but well reviewed!) tool (This one: https://www.banggood.com/MGEHR1212-2-Ex ... 53298.html) for some experiments. Well, I can profile with it, but the finish isn't great, and I get some vibration. But perhaps that's just a reflection of the tool quality.

So, short of making my own collet chuck (which is difficult because of the unknown spindle nose geometry), I'm not sure how to proceed. What do other people do?

Thanks!

Luke

Pete.
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Re: Turning parts with features on reverse

Post by Pete. » Fri 26 May , 2017 15:12 pm

Why do you say the the spindle nose geometry is unknown?

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Re: Turning parts with features on reverse

Post by TDIPower » Fri 26 May , 2017 17:01 pm

Hi could I just ask did you get the 1212 sized tool? can you tell me what the TMax is on that is it isn't in on the list. The tool I have with my Starturn 5 just has the push in insert and I don't feel confident with this for any more than grooving (although the Denfrord software seems fine to want to use it) From my research the tool holders that just take the push in inserts are just for grooving but the ones like you posted and take the 'dog bone' insert can be used for profiling as the insert is clamped

Thanks

Pete

lsteele
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Re: Turning parts with features on reverse

Post by lsteele » Sat 27 May , 2017 12:17 pm

Pete -

Well, I've looked around at various times and it seems like no one is quite sure, although I have ideas about making a part to fit, it would entail quite a lot of trial and error.

e.g. viewtopic.php?f=43&t=2890&start=20

TDIPower -

Will check

Pete.
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Re: Turning parts with features on reverse

Post by Pete. » Sat 27 May , 2017 12:58 pm

Right, well since Paul Compton says in that thread that it compares to DIN 55021 with it's 7.125 degree taper angle (which happens to be 1:8 taper), and since that taper angle is exactly the same as camlock, and since Denford supplied lathes with d1-3 camlock taper, it's a fairly reasonable assumption that they would have a machine set up for cutting those 1:8 tapers and that's what they used.

Camlock taper backplates are not hard to make, I have made several so these should not be either. I cut the taper using a feeler gauge to check the gap. All you have to do is remember that every thou you take off the taper you move the backplate 8 thou closer to the face. Quite often I over-shoot then end up facing the back for a proper fit. Another thing to remember is that the camlock WILL pull in the taper slightly just like tapping home a morse taper drill so there's a bit of allowance there too.

Pete.

lsteele
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Re: Turning parts with features on reverse

Post by lsteele » Sun 28 May , 2017 11:22 am

Hi Pete,

Thanks for that suggestion. So let me just try and flesh out some of the details because I've never tried to machine a backplate. As I see it I've have to chuck the material for the backplate, then machine the taper with the maximum OD at or fractionally under the desired diameter. Then I'd have to take the chuck off (with the machined material still clamped in the chuck), offer it up to the spindle nose and measure the gap with a feeler gauge, then use the measured gap to calculate how much further to bore out the taper. Then once I've got a good fit, clamp the plate to the spindle, and turn the mating spigot required for the chuck.

Is that about it?

Thanks!

Pete.
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Re: Turning parts with features on reverse

Post by Pete. » Sun 28 May , 2017 13:00 pm

That's it, it's a bit of a long-winded process especially with a bolt-on chuck mount. Get it close and use a pair of same-size feelers to measure the backplate gap. keep going up in sizes until the feelers are snug both sides then check that you haven't jacked it off the taper by Say you have 5 thou gap, then you need to take 5/8= 0.000625" (six tenths) off the taper. Have a tenths-reading dial gauge reading off the back of the cross-slide so you can dial it right in on the money and cut the taper again.

Then if you're as successful as I was you can have another couple of goes at it until you get it right :D. Remember, if you get it down to 1 or 2 thou gap it'll pull in on the bolts.


A better way of doing it, if you have a spare backplate/faceplate etc (or another lathe you can use), is to turn up a dummy spindle end and check it with bluing on the spare backplate. then you can use that dummy end as a gauge to avoid having to dis-mount the chuck every time. Turn it between centres so that when you use it as a gauge you can use the tailstock to hold it true, saves you having to use two feelers.

EDIT: Joe P video for setting accurate angles on your compound. I like his videos because he gets right to the point and doesn't drag them out.

https://www.youtube.com/watch?v=YCllVu4K738

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Re: Turning parts with features on reverse

Post by DavidB » Sun 28 May , 2017 17:15 pm

When I set-up to do my ER40 chuck I'll also be machining the taper out in my Orac 3 jaw backplate because I'm not happy with the fit as it is currently. At the moment when it's placed on the spindle the gap is about 0.4mm between the faces and while it can be pulled on so the faces meet it's much tighter than I would like it to be. All the D1-4 mounts I have for my M300 are far closer so I'll aim for a minimal gap when re-machined.

lsteele
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Re: Turning parts with features on reverse

Post by lsteele » Thu 01 Jun , 2017 15:33 pm

David, it sounds like you've done this before?

Two more questions spring to mind - can the 3-jaw hold a large enough diameter for a backplate? And I read somewhere that it's difficult to get the carriage close enough to the spindle to machine the backplate on an Orac - any truth in this (haven't tried to see how close I get get the carriage to the spindle nose yet)?

Cheers,

Luke

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Re: Turning parts with features on reverse

Post by DavidB » Thu 01 Jun , 2017 18:46 pm

Luke,

Actually I haven't for a short taper nose chuck mount only a long taper nose L00 fitting for a Kerry 1140 I have. My Harrison M300 came with 4 D1-4 camlock items and I've added another 4, 3 of which I bought chuck mounts for and added the rest, the ER40 chuck came with an integral D1-4 fitting. That's 8 D1-4 mountings I have experience with fitting and I would say they are all spot on at around 0.1mm gap before the camlocks are engaged to pull the faces together, even the cheapest D1-4 mount with turned rather than ground taper fitting is spot on. While the D1-4 mounts aren't cheap, though not necessarily expensive, I'd rather buy them as they're readily available, the reason I'm making the Orac mount for the ER40 chuck is as others have found it is an odd size and not available off the shelf unlike the D1-4.

I have the ER40 chuck with its mounting plate fitted to it and fitted to a precision test bar which I will mount between centres and machine on the M300, that will allow me to take it out and check the fit on the Orac spindle. I'll rough machine the taper close to size then swap over to grinding the features to final size. I'll do the same when I correct the 3 jaw mount although the precision test bar won't fit the 3 jaw so I'll either have to buy a smaller one or carefully machine a suitable arbor to mount it on myself, it after all a 3 jaw and not a high precision one, I'll tighten it up with the master 0 jaw and see what the run out of the mount is like when fitted to its arbor and report back with some pics of the ops. No idea about your question about machining the backplate on the Orac, I would think the chuck would cope with the OD being only slightly larger than the chuck in my case and using outside jaws but can't comment on whether the backplate fitted to the spindle can then be machined for mounting the chuck.

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