Lathe Tool Grinding Helper

[rleete]

Having never turned or machined nylon, I can't offer any meaningful comparisons. Glad you seem to have it sorted out.

[randyc]

A brief update:

I gave up waiting for a few warm days (as if that's going to happen) to get back to the diamond grinder.  Yesterday I ordered two 1500 watt electric space heaters, the presumption being that with one on either side of me, I may be able to get something done.

A horrible waste of electricity which I'll make up for by wasting a horrible amount of time.

 

[randyc]

It is COLD out there but I put on several layers of clothing, surgical gloves and went out to the shop for an hour to finish up the legs.  This will be the last trip until the heaters arrive !

I wanted to angle the legs out slightly from the grinder table; fifteen degrees looked about right when I tried different angles in the CAD layout. In the following photo a leg that was parted off on the lathe, is installed in a collet block. (Have I previously mentioned that this is nasty material ?  The end mill is making the first pass across the end of the leg - look at the size of the burr it has raised !)

A fifteen degree angle plate in the mill vise is held in position by the vise stop, as shown. The collet block rests snugly against the angle plate as the legs are milled to length at a fifteen degree angle and piloted for 1/4-20UNC-2B perpendicular to the fifteen degree angle.

   

After the milling operation the 3/8 end mill was changed to a 3/16 end mill for producing a pilot hole for the 1/4-20 threads. I could have used a slitting saw in the mill, BTW, to cut the legs to the correct length at fifteen degrees but my saw arbors have larger shanks and would require a change of collets, entailing cranking the knee up and down'

The two end mills used had 3/8 shanks - no collet change required and the knee doesn’t have to be lowered/raised. The larger end mill was used to cut to length at the correct angle and the smaller end mill for a pilot hole.  It's often useful to recall that plunging with an end mill, if carefully done, will always produce a straighter hole than drilling (note that a possible exception is gun-drilling) because plunging is a boring operation for all practical purposes.  In fact, many of us use end mills as boring tools in the lathe.  

Normal tap drill diameter for 1/4-20 would be about .201 diameter but as noted, a .201 drill plus drill chuck would require cranking the knee up/down to remove/reinstall the end mill and the drill chuck.  Naturally I wanted to cut the angle AND produce the hole in the same setup so that the hole would be perpendicular to the angle.

I had no re-ground end mill to produce the right pilot hole so the 3/16 end mill was used to produce a pilot diameter that could easily be reamed out with a .201 drill, by hand.  (The existing plunged 3/16 hole could have been used as-is for tapping in this soft material but why make tapping harder than it needs to be ?)

An old keyless drill chuck attached to a shop-made handle is convenient:

Hand reaming with drill

   

De-burring with counter-sink

   

Tapping

   

Incidentally, since I mentioned not liking to crank the knee up and down (who does unless there is "Z" axis power feed ?), I'll point out something that occurred to me many years ago.  One day, after lifting the knee for about the thirtieth time, I started thinking about a way to minimize that effort.

I noticed that the typical R-8 collet has a grip length of about 3/4 or maybe 1 inch.  The dim little light bulb in my head flickered for a moment when I noted that all of my drill chuck arbors were 3 and 4 inches long !  Immediately, I cut them all down to about an inch and saved about three inches of knee movement to insert and remove the chucks.

   

Further, I made some new arbors and shanks (for tooling that I used the most in the vertical mill) standardizing on 1/2 diameter.  This covers most end mill sizes that I normally use so to change over to a drill chuck, for example, it's necessary only to drop the knee about a couple of inches because no collet change will be required - all tools for a particular task having the same diameter shank.  Obviously this will not always be possible but you'd be surprised at how much less cranking (and time expended) is required.

After tapping the 1/4-20 holes, I needed to round the ends of the legs so back they went to the lathe. I used a tailstock center to support the legs because a forming tool would be used to round the ends. Forming tools exert more pressure, of course, than a normal turning tool.

Increased cutting tool pressure at the end of a cantilevered, flexible part would likely result in a scrapped part unless the part is well-supported. But one cannot cut to the center of a workpiece supported with a conventional tailstock center so a “half-center” was used.

As shown in the photo, almost half of the end of the center is ground away to allow the cutting tool to plunge all the way to the center-drilled hole in the work. (FWIW, it can be seen that this dead center is made from two different materials. The working end is carbide , brazed to the heat-treated shank and ground to dimension.)

   

At this point, the motor must be removed so that the ¾ inch table can be machined. That’s going to wait until I receive the space heaters and verify that they will toast my old body to a functional degree. At present this is the concept (sheet metal panel and grinding wheel guard not shown):

   

Cheers !

[randyc]

It was a very pretty day here on the ocean so I opened the garage door to let the shop warm up and then put in a couple of hours on the project.

The ¾ inch thick baseplate has been sawed to the dimensions in the CAD layout. I made a rough layout of the hole pattern on the protective film covering the jig plate. Although I use the dials on the mill to establish hole locations, sometimes I lose track of the number of turns and the layout prevents making an unrecoverable error.

After drilling, each fastener hole was counterbored, exchanging the twist drill for the counterbore and then re-installing the drill at every location. I was reminded that changing tools in a standard Jacobs chuck was a huge PITA, years ago. Thank goodness for the advent of Albrecht/Rohm style chucks !

   

Just for appearance, I wanted the end of the base plate to be round and when I envisioned it, the process seemed simple enough. As I thought more about it, I realized that it was going to require a little more work. My plan was to slowly rotate by hand, the base plate against an end mill, the desired pivot being held in the milling vise. (This would be similar to rotating the compound on a lathe to turn concave and convex shapes.)

To create a pivoting point, the baseplate was first drilled and bored. Next, a steel bushing needed to be turned/bored for a tight fit with the pivot bolt (which was just a long 1/2-20 bolt with a nice smooth shoulder) and a press fit with the plate bore.

   

The reason for the bushing is to prevent galling and seizure that would likely occur if the aluminum base plate was pivoted directly against the steel pivot bolt. I reasoned that a VERY tight fit between the pivoting surfaces was required to prevent chatter. Incidentally, at completion the pivot hole will not be visible, the tool holder will cover it, no matter the position of the tool holder on the base plate.

The base plate could be removed now and set aside temporarily.

I used a few pieces of scrap to make a multi-layered assembly, a “sandwich”, for clamping the baseplate while allowing it to rotate around the pivot. The “sandwich consists, first, of a rectangular piece of steel for gripping in the milling vise, to which the pivot bolt is welded.

   

A scrap of 1/8 thick rubber was punched to produce a ½ inch hole:

   

The is the "sandwich" excluding the aluminum base plate.  It consists of the pivot plate, a rubber friction pad, a clamping plate and of course a nut.

   

The bushing (the function of which was described previously) was turned for a heavy press fit in the aluminum base plate and bored for a very tight fit with the pivot (the pivot is the body of the bolt welded to the steel scrap, not the threads).  Note that a shop-made adapter was used in the boring bar to accommodate small cutting tools, in this case a 1/4 inch HSS tool ground for boring.

   

OK, if you’ve suspected that I was winging it, you are exactly right ! All of this was just intuition since I’d never tried milling something by hand-feeding previously.

Pressing the bushing was too heavy for my small one ton arbor press so I simply pulled the bushing into the plate using the pivot bolt and a nut rotated with a long breaker bar. All done, note that the pivot bolt shoulder was such a tight fit with the bushing that it had to be tapped into place with a rubber mallet which was exactly the type of fit that I desired.

   

The baseplate, rubber pad and clamping plate were installed over the pivot plate in that sequence and clamped in the milling vise. The rubber pad between the clamping plate and the base plate protects the finish of the plate but more importantly provides friction as the plate is rotated against the end mill.

Friction is desirable so that rotation of the plate will be slowed, preventing too fast a feed. Friction can be adjusted during the cutting process by tightening/loosening the nut that applies clamping pressure to the “sandwiched” parts, functioning exactly like a brake. Here is the assembly minus the nut.  The mill spindle is being centered over the pivot point.

   

After centering, the “Y” axis is locked, it is now on the pivot bolt center line and the table shouldn’t be moved in this axis again.

The “X” axis is craked over so that the end of the baseplate is near the cutter and the rounding process begins. I initially considered supporting the plate with machinists jacks but didn’t. My reasoning was that the helix of the end mill would tend to lift the plate, not push it downward.

I decided to make a pass or two and see if there was excessive chatter. If so, I would need to make something to support the plate from above. I hope that this makes sense. It turned out that no support was needed; when the plate started “shuddering” I simply tightened the pressure on the rubber friction pad until the chatter ceased.

As can be seen, I added a large wood clamp to the set-up. After trying a pass or two without it, the lack of control when rotating the plate allowed only light cuts to be taken and I was impatient. Addition of the clamp not only added leverage but spread my hands apart placing them in a position that allowed much more control. (Also seen in the photo is a socket wrench installed over the nut that holds the assembly together. At several points during the milling, I had to tighten the nut.)

From here on out, I took 1/8 deep passes at an estimated 10 ipm and the chips were flying out like a water hose ! NOTE: I would NEVER try this with ferrous material unless taking the very lightest of cuts. In fact I don’t recommend this process at all for inexperienced folks !

   

There wasn’t much of a problem making a conventional cut on the part but a climb cut of more than a few mils would NOT be a good idea, even with the “brake” that I devised. I note yet again that this is a risky operation and would better be performed in a rotary table. I read about it one time and just wanted to try it as a technique that might be useful in the future. If it isn’t obvious, one wants a lot of mechanical advantage to pull this off and very light cuts are advisable.

The distance from the pivot point to the cutter needs to be quite a bit less than the distance from the pivot to where the rotation is being applied, for leverage and control. As mentioned previously, the pivot interface was very tight, with as little clearance as I estimated could be achieved while still being able to rotate the part. If the pivot was sloppy, it would have shown up as poor surface finish on the milled edge.

Here is the plate at present, protective film still sort of in place. Needs a bit of sanding to clean up the milled surface after which I think that I’ll break all of the edges on the router table. Although the surface finish is not the best, I consider it pretty good for the technique used, LOL.

   

[f350ca]

Well done Randy. I've used the same technique to round the end of control arms made of steel but MUCH smaller scale.

[Highpower]

(12-30-2017, 12:17 AM)f350ca Wrote: Well done Randy. I've used the same technique to round the end of control arms made of steel but MUCH smaller scale.

Dale Derry has another interesting way of cutting a radius. https://www.youtube.com/watch?v=hTj6LC6agrg

[f350ca]

Interesting way to do it. Wondered how he was going to get the end. Will keep that one in the memory bank.

Thanks

[randyc]

This is nitpicking but the technique produces an approximate radius and would require quite a few passes to make it look good.  Time consuming when the mill spindle is stopped between cuts, as it should and which he noted.

Impractical for radii greater than about two inches (limitation imposed by the vise jaw dimensions).  Impossible for long parts.  Method always requires a hole for the dowel pin which is not always possible.

I loved his comment "Every day is a school day in the machine shop" !!

[randyc]

This is an update, well actually a downdate since nothing has happened in the shop since late December.  But maybe that's a good thing because the next grinder part to be made is slightly challenging for my stone-age-capable machinery and has made me think about upgrading the vertical mill to around the nineteen eighties or so, LOL.  The part looks like this:

   

Simple enough, right - rotary table job ?  But for a 73 year old, 5' 5", 128 pound man with one lung, lifting a thirty pound vise off the table to install the fifty pound rotary table is something that I choose to avoid when possible.  My normal procedure is to calculate X, Y coordinates from the bolt circle dimensions then use the dials on the crank wheels of the mill to position the table.

But there is a reasonable possibility of messing up the hole pattern (the part is made from a big chunk of Delrin and I only have one piece) because of this manual technique.  It's happened before even though I've been using only dials for a l-o-n-g time.  I'm probably exaggerating the possibility of messing up the part, ha-ha-ha, because I've convinced myself that it's time to install a DRO, especially since the cost of these things has dropped dramatically !

   

I've looked around for a while and haven't found a DRO system with the appropriate scales to fit my 8 x 30 mill.  Of course the immediate reaction is to order the scales oversize and whack them off as desired.  But everyone I've talked to assured me that it's not a good idea.  I've cut a moderate amount of glass including many cylindrical shapes that are more challenging than a flat surface so I wondered if the advice wasn't overly conservative.

I looked on the internet and found several videos of guys who also thought that this operation should be reasonable.  S-o-o-o- I'm going to try it and I'll document the process in case there is interest, even if failure makes me tuck my tail between my legs, ha-ha-ha

[f350ca]

You'll like it Randy. Just installed a 3 axis on my mill. Direct from China the price is ridiculous compared to when I bought the mill. They even calculate the hole positions for you.
Out of curiosity, why not order the right length scale? The company I bought from had them in 50 mm increments or they'd custom make them any length for you.

Greg