PM-727m New mill has arrived!

[Sloth2009]

Playing around with HSS. My one previous bit grind didn't cut too well with a fly cutter on Al. I realized I hadn't cut in a rake angle at all so I reground and added one. I am also now wondering about the nose radius? Is it too small? Any grinding suggestions?

 

[Bob Korves]

Nose radius can be small or large, as needed. First, you should always have a radius, even if it is very small. Otherwise the tool will chip. A small radius is good when you want to push the tool less hard. That might be to minimize deflection on a long and slender part, or when your machine is under powered. A big radius is for a good surface finish, or to make a large radius corner. If your machine or setup is not rigid enough to power the larger cutting area, you may get chatter, or bog down the lathe if it is not powerful enough. That is a nice thing about HSS tooling. You can easily make the tool match the circumstances, and keep tweaking it until it works good.

 

[Sloth2009]

My powered x-axis is still on back order from PM. I decided to cancel that for now and ordered the 3 axis Dro through PM. I think it will be money well spent. I have next week off. I plan to do the epoxy tram on the column. Wish me luck.

 

[Sloth2009]

Oh. I got my aluminum t-slot covers today and fit them in. Oddly the t-slot in the front of my table is slightly wider than the back 2 and the covers fall through. I just stacked 2 covers on top of one another and they fit perfectly. The way covers slide pretty easily. I may put a little tape on the side of them to increase their staying power.

 

[Sloth2009]

The placement of the wires on the back of the pm727m switch box are annoying to say the least. They are right in the way of the z-axis locks and of one of the head locking bolts. I bought some 90 degree cable glans to change the output direction of the wires, but realized there is an even easier fix. Simply turn the power box back plate upside down! I may add a small eye bolt to the back of the colum or something similar to guide the power cord as the head moves up and down.

 

[fradish]

Turning the backplate upside down is a good idea (which of course I didn't think of...)

I made round aluminum knobs for my z-axis locks because I was running into the same issue.
Plus I'm not a fan of the spring loaded locking levers that come on the mill. I even prefer the
hinged locks on the y-axis to the spring loaded locks. Just a personal preference.

I've replaced my x-axis locks too as they would sometimes interfere with the base. I've never
found that I needed to tighten these more than hand-tight, but even if I did I used socket
head cap screws so I can tighten them with a hex wrench if I ever need more leverage.

 

[Sloth2009]

Well... I did the epoxy tram today. Now time to wait 24 hours and do some testing. Here is an outline of the process I used.


PM-727m DWH Epoxy Tram

Phase 1: Initial Setup

Buy and install 4 longer 12mm bolts
Pull mill from wall for 360 deg access
Level table by adjusting mobile base
Clean machine and chip tray of chips and oil
Remove way covers
Loosen bolts and rock column from front to back adding larger shims during each tilt
Aim for at least 1" gap to make cleaning critical surfaces easier


Phase 2: Critical surface Prep

Clean mating surfaces and around column base
Wipe down with isopropyl alcohol and acetone
Scrape off any paint or Chinese putty
Use 120g sandpaper to roughen critical surfaces
Clean critical surfaces again with acetone
Install at least 2'layers of double sided foam tape to prevent epoxy from leaking to inside of column


Phase 3: Gap setup

Lower column to about 1/2" gap
Install original bolts
Install 2 copper crush washers on each bolt
gap = 0.090" good thickness for DWH
Lower column onto copper washers
Lightly snug down bolts


Phase 4: Masking off

Clean areas to be masked off
Tape off large gaps in front rear of column with painters tape
Tape and off column, base and chip tray where needed


Phase 5: Epoxy injection

Install test indicator and tram column roughly to table
Temperature ok for epoxy?
Mix epoxy and hardner for 3 minutes
Inject prepared epoxy evenly into gap
Tape gaps to keep epoxy from running out
Tram z to table with square using column bolts to change tram
Do y axis 1st then x... then y again.
Be as precise as possible especially in y-axis
Let cure 24 hours

 

[jbolt]

Curious if you used any kind of mold release on one side of the mating surfaces you epoxied in case you ever want or need to remove the column?

 

[Sloth2009]

Curious if you used any kind of mold release on one side of the mating surfaces you epoxied in case you ever want or need to remove the column?

No I ended up deciding against it. I did think about it quite a bit. I originally wanted to wax or teflon grease just the bottom of the column so it could be separated if needed.

First I figured it would be fairly difficult to get a thin even layer of release on the upside down surface without some way to lift the column completely off the base. I did this tram 100% myself with only manpower, so it was difficult already. Second, I thought the adhesion of the epoxy to both surfaces would add some more strength in tension as well as compression at the joint. Essentially adding stronger and more even downward holding power than the mounting bolts alone. I'm still not entirely convinced that line of thinking is correct and I may regret it later. It definitely made the tramming a bit more stressful.

I ended up not filling the gap in the front of the column. I couldn't get the syringe in the right place to inject. I could fill this in later if I want, or leave it open in case I need to go at it with a crowbar.

At this point there are a few things I would have done differently. I should have found a short thin piece of tubing to attach to the syringe tip. The syringe tip by itself was too short and wide to fit very far into the gap. I also would cover all the gaps in strong clear packing tape before injection. Poke a small hole in it with a screw, inject through the hole, then tape it back up when done. I figured this out 3/4 the way through injecting after making a mess. 3 or 4 injection holes along each side would do the trick. Make and plug the holes as you go to reduce mess. The clear tape lets you see the gap fill up as well. I used 2 50 DWH kits along with 2 injection syringes. With my mess, I just barely had enough to fill the 3 sides.

 

[Sloth2009]

As a little side test, I lightly greased a HSS tool bit and shimmed it into my fly cutter. There was a slight gap at one end due to poor machining. When I mixed up the epoxy earlier I squirted a tiny bit in the gap. I just checked it out and it seemed to have worked pretty well. I think I will wait the full cure time to check out the mill though.