Author Topic: ADJUSTABLE BACKPLATE  (Read 4203 times)

Offline Don1966

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ADJUSTABLE BACKPLATE
« on: August 04, 2015, 12:31:54 AM »
Since replacing the bearings in my Myford Spindle I set out to get things to run as true as possible. One way was to make an adjustable backplate for my Chuck. We start out with a piece of cast iron and  cut it to the dimenision of my Chuck.
In the first photo I am cutting an opening to fit the original adapter plate which we will turn down to 2.75" at a depth of .375".

Next was to turn the adapter plate to .020" smaller then the opening in the adjustable backplate.

Using the DRO function I drilled the mounting holes in the adapter plate and adjustable backplate.

After assembling I mounted it to the lathe and faced it true to the lathe axis and finished cutting the outside diameter to the chucks diameter.

I needed to drill the adjustment holes and tap them after final dimensions.

After making three 1/4x40 screws out of tool steel they were hardened. The Chuck was mounted to the lathe and trued with the three adjusting screws.

After doing the alignment on the Chuck I till seem to have play in my spindle even with it adjusted as far as I can get it. I am beginning to think my front spindle bushing is oval shape like Gray had said. I will investigate this tomorrow. I do have a new bushing but will have to make a tool to remove it with and a tool to reinstall the new one.

Don

Online b.lindsey

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Re: ADJUSTABLE BACKPLATE
« Reply #1 on: August 04, 2015, 01:06:45 AM »
Don, that is a nice project for your Myford. When truing the chuck, do the three SHCS's holding the original adaptor to the new backplate need to be semi-loose to allow the adjusting screws to move one relative to the other. If that is the case, I am wondering how you then tighten them without removing the whole thing (chuck, backplate and adaptor). Doesn't seem like there would be enough clearance to get an allen key in from the backside while mounted on the lathe. Just curious as to the actual setting process.

Bill

Offline Don1966

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Re: ADJUSTABLE BACKPLATE
« Reply #2 on: August 04, 2015, 01:25:20 AM »
Hi Bill, to answer your question a special wrench is made with a cut off from an Allen wrench and silver soldered to a piece of 3/16" x.5" strip of metal. Then the end Is rounded off to make it all fit. The SHCS screws are losses just enough I allow the three screws to push it in place. By the way the three adjustment screws are lined up with the Chuck jaws.

Don

Online b.lindsey

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Re: ADJUSTABLE BACKPLATE
« Reply #3 on: August 04, 2015, 01:27:56 AM »
Got it!  Thanks for the explanation my friend :)

Bill

Offline sshire

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Re: ADJUSTABLE BACKPLATE
« Reply #4 on: August 04, 2015, 02:01:05 AM »
On the Bison Set-Tru 5C, the mounting bolts are inserted thru the front of the chuck. The backplate is threaded. When I adjust it, the mounting screws(SHCS in counterbores)  are backed out just a bit, then the adjustment is made and the mounting screws are re-tightened.
Easy
Best,
Stan

Online Jo

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Re: ADJUSTABLE BACKPLATE
« Reply #5 on: August 04, 2015, 08:14:01 AM »
I am not sure if I have got this right the adjustable bit is used to correct the misalignment between the register on the back of the chuck and  the point of concentricy of the jaws :noidea:. Do you have to check concentricity for both sets of jaws? I can't see myself fiddling with the setting each time I swopped between jaws.

Mr Silky's new Bison 4 jaw SC I picked up mounted directly on a register and it came in at under 0.01 mm run out so I am calling that acceptable. I am still unhappy with those horrible grooves wobbling in and out on the outside face of the standard jaws  :facepalm2:

Jo
Usus est optimum magister

Offline Tjark

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Re: ADJUSTABLE BACKPLATE
« Reply #6 on: August 04, 2015, 11:06:27 AM »
Don a nice solution to  the problem off the run out.
Have seen some chucks who have this build in the chuck back plate.
I have a chuck with the wescot system.
Do not use it often because the trouble Jo mentioned.

     Tjark.

Online BillTodd

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Re: ADJUSTABLE BACKPLATE
« Reply #7 on: August 04, 2015, 11:10:06 AM »
I use old Cushman that I modified to be adjustable and a burnerd griptru for sunday-best .

The cushman is mounted to the back half of a hardinge chuck that carries four pins. The pins fit into holes in the chuck body and are pushed back and forth by grub screws from the side of the chuck body.

It's as easy to adjust as a four jaw and will repeat to better than a thou" on the same diameter.

Since taking the pictures, I've drilled mounting holes from the front to make it easier to clamp tight.
« Last Edit: August 04, 2015, 11:22:03 AM by BillTodd »
Bill
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Offline Don1966

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Re: ADJUSTABLE BACKPLATE
« Reply #8 on: August 04, 2015, 06:28:18 PM »
Well I find that adjusting the run out quiet simple to adjust and I do less .001" TRO.


Don

Offline Overbuilt and Overkill

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Re: ADJUSTABLE BACKPLATE
« Reply #9 on: August 15, 2015, 04:44:37 AM »
Don,
Done in the finest old school Model Engineer tradition in my opinion. And I'd expect nothing less after looking at your photo album. Anyone who can build George Thomas's VDH and UPT to the level you seem to have done would build a set true type of chuck mount the way you have.

Jo,
I don't know if you ever got your exact question answered. These set true type of chucks are meant to be used for at least more than one part that are all the same diameter. Multiple parts would be even better and justify the time spent setting the chuck to that diameter for very low to zero runout. How Don built his can be done for 3 jaw, 4 jaw self centering, and even collet chucks of any kind. But they are generally designed to semi replace the need for collet chucks since in theory you could adjust a good 3 jaw or those 4 jaw self centering chucks to a repeatable zero runout situation at that exact part diameter. I think it's a great addition to any chuck mount that uses a backplate since it does allow you to fine tune any part to whatever accuracy you feel you want given enough time for the initial setting. And you can use it or not and it really doesn't hurt or hinder the operation of any chucks operation that I know of. But even very high quality 5C or ER collets and there chucks aren't 100% perfect if your machines bearings are of that same high enough quality. So that set true design like Don has done gives you that last bit of perfection if you want or feel you need it when the parts justify the accuracy.

With a lathe that takes a direct mount 5C in the spindle then this style obviously doesn't work. But you'd already know that. Others might not.

Greg