Machining Setup's with Few Comments

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Sat Sep 29, 2018 7:24 pm

Machining thin accurate washers.

There are many ways to do this which have been described on the internet but I will add my experience here as there are always a few new twists involved.

Recently, I started to make a number of live steam locomotive parts, one of which was to make 24, 3/8" OD by 1/8" ID by 3/64" (0.047") thick bronze washers. The washers needed to be +- 0.001" both on thickness and on parallelism.

I choose to construct and use a simple shop made pot chuck to hold the partially machined washer blanks to achieve the above. The design is described in Joseph W. Serafin's book "The Metalworkers"s Benchtop Reference Manual". There are lots of used, reasonably priced copies of this book on the market.

I happened to have a convenient length of 1/2" nominal steel tubing (which miked 0.501" OD) and 11/32" on the ID. Make the pot chuck as shown in the first photo. The pot chuck recess should have a truly square end and a truly flat bottom. For this job, I made a 1/32" wide sawcut and the locking screw is a standard 6-32 NC fastener threaded into one wall of the steel tube with a clearance drill in the other. Make the recess a close slip fit to the OD of the washer.

Machining the washer blank (OD/ID and one face) should pose no problems. Put a barely visible chamfer on the outer washer blank face and debur it thoroughly.It is important to have absolutely no burrs anywhere.

The second photo shows how the washer was removed for checking thickness purposes and the aligning marks on the pot chuck body and its associated collet.

To ensure that the partially machined washer blank sits truly square in the pot chuck, use the lathe's accuracy for this purpose as seen in the third photo.

The drill chuck jaws are lightly pushed against the outer washer face while the lathe spindle is rotated by hand (with the pot chuck clamping screw just set snug) and then a little bit more pressure is applied through the tailstock barrel. Then tighten up the pot chuck clamping screw.

Using the above technique, one can take the washer in and out of the pot chuck as machining proceeds to check the washer's thickness and put it back and have it run dead true again.

The last photo shows the first successful production washer (the upper washer) and a test washer. I destroyed three test washers before I came to the above.

I have not described my technique to the live steam boys so they won't know how I did it unless they read this post.
Attachments
400 Simple Shop Made Pot Chuck.jpg
401 Aligning Marks on Collet and Pot Chuck and Used Razor Blade to Remove Washer.jpg
402 Using the Lathe Tailstock to Ensure that the Washer is Squarly Seated in the Pot Chuck.jpg
403 Test Washer Lower, First Good Production Washer Upper.jpg

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Tue Jul 02, 2019 8:44 pm

Optical centre punching - the good, the bad and the ugly.

This is for those who do not have digital equipment.

What you need - good eyesight, very good lighting and a very steady hand. If any one of the foregoing is a problem, optical centre punching is not for you.

What can you achieve? If you are very careful, you can get to within 0.001" - 0.002" of the layout line intersection. But it takes practice.

The optical centre punch which I have has a small black line circle with a tiny (and I mean tiny) centred black dot. The dot is much smaller than the width of the layout lines so one has to carefully centre the dot within the line intersection. The optical sighting is through a clear solid polished plastic rod so one must be careful to keep the plastic free of scratches and clean on the ends. Do not use any type of abrasive here no matter how gentle. Also, be aware of where you put or lay down the optical rod. The optical centre punch body is highly polished black anodized aluminum having a built in anti skid base. The fit of the optical rod and hardened alloy metal punch in the body of the centre punch is an extremely close but free sliding fit.

It would have been a better design if fine circle crosshairs with the circle (but not extending to the centre dot) had been included as well on the optical end but I guess this would have added some additional cost.

The main problem as I have experienced it is with the external lighting needed. Ideally, any lighting needs to illuminate the central dot and the layout lines without casting any shadows. One has to adjust the external lighting quite a lot to achieve this. A lot of the time the central dot just seems to disappear so one is constantly fiddling with the lighting looking for the dot. The unit is very sensitive to this.

Once the dot has been centred on the layout lines, the optical rod is replaced with the alloy steel punch. The smaller the work piece located under the optical punch, the more difficult this replacing movement becomes so a very steady hand is required.

And, with use and with the difficulty of metal being punched, the finely pointed and polished alloy punch end begins to dull so at some point it will need to be replaced. I punch using a non metallic 4-6 oz hammer seen in the photo and only a moderate blow is required to produced a well defined punch mark.
Attachments
602 Center Punching a Heart Shaped Link Blank with an Optical Center Punch.jpg
603 The Center Punch Mark on the Blank.jpg

Mr Ron
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Re: Machining Setup's with Few Comments

Post by Mr Ron » Wed Jul 03, 2019 11:38 am

:D Thank you Carrdo for the series. This is the first time I visited your thread. I did it out of curiosity and glad I did. I learned so much more about machining. Building a Quorn , I know is far beyond my capability. The thread about making and using a pot chuck for thin washers was right up my alley for new knowledge. I will follow your threads in the future. The photos were exceptional.
Mr.Ron from South Mississippi

Mr Ron
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Re: Machining Setup's with Few Comments

Post by Mr Ron » Thu Jul 04, 2019 1:12 pm

Carrdo wrote:
Sat Sep 29, 2018 7:24 pm
Machining thin accurate washers.
I suspect you put bar stock in the lathe, drilled the ID and parted off slices, truing up each new end surface until all pieces were cut off; then to the pot chuck for the finish cut. Is this how you did it?
Mr.Ron from South Mississippi

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Thu Aug 08, 2019 11:56 am

Yes, exactly.

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Thu Aug 08, 2019 2:44 pm

My "fancy" method for fitting a semi finished cast iron chuck backplate to a 3 jaw chuck body.

First of all, I only have recognized European, Japanese or American chucks and chuck backplates. I still don't think that far east products measure up but one can decide for yourself on this.

Second, I fit my backplates very tight on the chuck body recess i.e. a tap fit which is tighter than a push fit. I do not try to make any of my 3 jaw chucks into a "setru" or an "adjustru" - one can but every time a different diameter workpiece is put into the chuck, one has to "dial in" the chuck again. To me, this is what a 4 jaw chuck is for so...

To know exactly what I am fitting, the backplate was a Bison semi finished cast iron plate threaded 1-1/2" - 8TPI for the 9" SB lathe and the 3 jaw chuck a 5" dia. TOS Savity. TOS Savity chucks are made in the Czech Republic and are not as well known here as the Polish Bisons. Savity is the name of the town in the Czech Republic where these chucks are produced. It was a standard, regular duty (not a high precision, heavy duty special) type 3 jaw.

I have a couple of TOS Savity chucks and they both are very well made and finished and always meet or slightly exceed their stated runout tolerances (when new).

To jump the gun here, after fitting, a 3'' long, 1/2" dia. ground dowel pin extended 2" out from the front of the chuck jaws saw a TIR of 0.0028" runout and the runout 1" from the front of the jaws was 0.0025" and at the jaws themselves 0.0019". I could really be measuring wear on the lathe bed here but I can't complain about what was recorded.

Not to be too long winded here, the most critical aspect of having the best possible outcome on a lathe with a threaded spindle is: "is the back face of the the chuck backplate truly flat, unblemished and truly square to the (centre hole) axis of the backplate?" If not, then your chuck will "wobble" when installed and there is not much you can do to correct this condition. One has to rely on the reputation of the backplate manufacturer here and that is why I only go with only a brand name (no guarantee but...).

If this is good, then do everything to keep it that way, no nicks, no scratches, no careless handling and don't jamb/snap the chuck backplate up against the lathe's spindle register flange and keep everything very clean.

The lathe's spindle nose register is the other half of this equation. The lathe's spindle register flange has to be ground dead straight and square to the longitudinal axis of the spindle. Quality lathe manufacturers go to extreme lengths to ensure this condition. This is the surface against which the chuck backplate's rear face butts up against when the chuck is installed on the lathe's spindle nose - and this is where all of the precision is. If this isn't right, nothing will run true ever. The unthreaded portion of the lathe's spindle nose and the threaded portion of the spindle nose are only guides - it is better if they are true close fits but it is not all that critical.

On my 9" SB lathe, the unthreaded portion of the spindle nose mikes 1.510" exactly. The Bison chuck backplate is bored out to 1.515" here (0.005" oversize), but when fitted to the late spindle the chuck runs true (within spec.) as it is the both the lathe's and the chuck's backplate face register surfaces which control the runout. I have SB factory lathe chucks where the gap here is 0.030" (!) and everything still runs true.

So, it is equally important to do everything to keep the lathe's spindle nose flange registry surface as pristine as possible, no nicks, no scratches, no abuse.

Examen the backplate registry surface and the back of the chuck body to be absolutely certain they are free of any blemishes. I very lightly ran a fine oilstone on the chuck's back face just to be sure.

Clean and install the semi finished backplate on the lathe's spindle nose. Rough and then finish turn the backplate spigot. I have a very tiny chamfer on the front of the backplate spigot. This lets me know when I am getting close to the finished diameter but I don't rely on it only. Measure and remeasure with your best and most accurate micrometers. Also, there is a tiny "V" groove cut in at the root of the spigot so there is no corner interference. And have your cutting tools razor sharp when making the final passes as having a tap fit means only a 0.0002" - 0.0003" clearance.

Finally, the depth of the turned backplate spigot should be slightly less than the depth of the recess in the back of the chuck for reasons which I will explain later.

To be continued.

PS: I have not included any photos of the above because it is just basic good turning technique. The photos which are here are my fancy way of locating/drilling the backplate bolt holes which I will explain.
Attachments
425 The Setup for Drilling the Chuck Mounting Bolt Holes on the Semi Finished Chuck Backplate.jpg
426 Drilling the Chuck Mounting Bolt Holes on the Semi Finished Chuck Backplate.jpg
427 The Finished Chuck Backplate and the 3 Jaw Chuck.jpg
428 The Chuck Backplate and the 3 Jaw Chuck Fitted Together.jpg

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Thu Aug 08, 2019 3:28 pm

Testing the overall chuck runout.

If you look carefully, you will notice that the OD of the chuck backplate has been left slightly larger than the OD of the chuck body.

This is so that there is a raised edge against which a piece of hardwood can be set against to tap the chuck off the backplate if ever needed otherwise if they were the same diameter one would never get the chuck off the backplate with the near interference fit between the two parts.
Attachments
432 Testing the Chuck Runout.jpg

pete
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Re: Machining Setup's with Few Comments

Post by pete » Thu Aug 08, 2019 5:54 pm

Fwiw one recommendation I've found mentioned in a few places and mostly by professional machinists is to use an oiled thin piece of card board doughnut shaped shim between the spindles locating register face and the chucks back plate for threaded spindles. Due to manufacturing methods paper or that card board is remarkably consistent for thickness. Using it helps prevent a stuck chuck on the spindle threads and is a safety for that happening if a serious crash were to occur. The card board will compress a bit and still prevent the friction lock between a hard metal to metal contact. The oil of course prevents rusting from the card board absorbing any water from high humidity levels and the oil helps to lubricate the metal faces and aid in disassembly.

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Thu Aug 08, 2019 8:42 pm

The SB lathe book says to chalk the flat ring face of the turned spigot on the chuck backplate, mate the chuck and the backplate together, separate them and the threaded backplate bolt holes in the chuck body will show on the chalked backplate. Locate the centre of each chalk circle on the chuck backplate and drill the bolt holes 1/16" oversize. Well, maybe...

I have done things this way (used line marking chalk powder to cover the flat ring face of the spigot) and it does work but sometimes I have first left a very thin film of oil around the bolt holes (add a small amount of oil around the bolt holes on the chuck body and then wipe it off before chalking the backplate - the minute amount of residual oil left is still enough to darken the chalk showing the hole more clearly if you leave the parts together for an hour or so).

Your experience may vary. I don't claim the above to be foolproof.

If you have the equipment, using the rotary table is a better method, as one only has to be able to locate one chalked hole radially (in one direction only) as the rotary table will accurately space all of the holes much more accurately than trying to manually centre on any chalk mark. But as usual, there is a price to pay i.e. one has to make the rotary table threaded adaptor and the rotary table centering plug seen in the first photo. As an alternative you can indicate the rotary table but I use many different kinds of made up centering plugs as I find them to be much more useful for quick and accurate centering and for many other rotary table operations such as end rounding. I only drill my bolt mounting holes 1/32" oversize and the bolts pass down through these smaller holes perfectly.

To make the double threaded adaptor is something else altogether. It has to be turned between centres (all over needs to be dead concentric) and each end threaded to gauge. As well, it has to be turned to be a dead ring fit in the unthreaded section of the centre hole my rotary table. And there need to be flats machined on it as shown in the photo as one needs to be able to get a wrench on it as it can lock in place very easily. I actually don't know how I ever did it as it was made decades ago. I did make a drawing and sent it to SB at the time and they confirmed that the 1-1/2" -8TPI end was within their tolerance specifications. On the other end is a metric thread which fits into the centre hole of the rotary table.

Since I will never make another one, I do everything to keep it protected using an old discarded backplate as a thread protector. I need to make a thread protector for the metric threaded end as well but that is for another day.

Finally, one should always mate only the two surfaces when the bolts pass through i.e. on the chuck body outer ring and on the outer ring on the chuck backplate in this case (there are other types of 3 jaw chucks where this is not the case i.e. with front bolt mounting rotary table chucks). The reason is you want the mounting bolts to tension against solid metal and not try to close a gap which would result in distortion of both the backplate and the chuck. That is why the depth of the backplate spigot should be slightly shorter than the recess depth in the back of the chuck body (in this case) which guarantees that the two flat mating surfaces are the ones where the bolts pass through.
Attachments
429 The Double Threaded Adaptor for the Chuck Backplate and the Rotary Table Together with the Rotary Table Centering Plug.jpg
430 The Threaded Adaptor and its Thread Protective Backplate.jpg
431 The Fitted Thread Protector.jpg

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Mon Aug 19, 2019 8:11 pm

Recently, I started on a locomotive part where the best piece of metal to use was a flame cut block of hot rolled steel.

Flame cutting of any steel alters the properties of the steel in the heat affected zone and not for the better in a home workshop environment as the heat affected zone is now glass hard and will rapidly destroy a HSS tool bit or end mill. The depth of the heat affected zone can be 1/8" or more so it is not just a matter of getting under the hard surface - one actually has to cut through it.

I do have carbide end mills but they are expensive and I am not going to use them up just to rough size a steel block.

Fortunately, I do have a 7" bench shaper which is not worked a lot but for this operation it is the ideal tool to use in conjunction with a braised carbide single point tool bit which one can buy very cheaply.

The bench shaper made short work of the roughing operation and I am very glad to have had it available for the job.

The secret is to maintain a short stiff (new) tool in the clapper head which itself should be well supported (centred on the ram) and have a fairly light depth of cut. I used between 0.005" - 0.010" DOC per pass depending upon whether I was end squaring the block (less DOC with the block being held vertically as seen in the last photo) or horizontally.

Then, just let the machine do its thing and work its magic with this miserable operation.
Attachments
433 Rough Shaping a Flame Cut Block of Hot Rolled Steel.jpg
434 The Flame Cut Steel Surface.jpg
435 The Same Surface after Rough Shaping.jpg
436 End Squaring the Block.jpg

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NP317
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Re: Machining Setup's with Few Comments

Post by NP317 » Mon Aug 19, 2019 8:29 pm

Nice.
I'm surprised you do not have the vice rotated 90 degrees for more secure holding of the part being cut.
But it appears your setup works just fine.
RN

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Carrdo
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Re: Machining Setup's with Few Comments

Post by Carrdo » Mon Aug 19, 2019 10:42 pm

Yes, it probably should be but interference with the passage way between machines as the shop is very crowded. People who know the place wonder how one can even move/make anything.

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