Mill table dual stop

[PeterT]

I have to do a lot of forthcoming internal pocket milling & that can be very tedious chore without some kind of stop to limit travel as you work your way down the material end milling (as opposed to watching dials and/or DRO position at each end of every pass). I made a similar system for my RF-45 mill & it worked out pretty good. The basic idea is you set the table to desired left position, set the left stop. Then do the same for right. Now when milling you can just traverse the table back & forth until it contacts the stops on either side.

My 935 mill has different dimensions so about all I could use was the concept & materials on hand. I have a power feed on the X so I removed the limit stop switch, wrapped its cord up neatly & just strapped it to the motor unit so its out of the way. Yes, the electric limit switches work pretty reliable but I find power feeding short lengths is more of a hassle than its worth. The spring limit bumpers just slide out of the Tee slot along the front of the table. The mill base was already drilled & tapped 5/16 for the center limit switch so I decided to make use of those holes.

 

[PeterT]

Here are the components. A chunky center stop plate (1/2" steel...cause that's all I had in 3" width), the left & right bumper plates (3/16 steel x 2" high x 2.5" long) and special tee nuts to accept them (steel). I made the bumper plates tall to maximize the contact area along the front of the table. The system cant take a hard hit without losing a couple thou, but I found by just tightening them reasonably I can easily get half thou repeatability multiple times by just walking the table in slow & kissing the center plate. The 3 (10-24) bolts is a bit overkill but a) it spreads the the load & clamps the plate securely just using an hex key on the cap screws b) I make use of this layout to make the round-over profile.

 

[PeterT]

Here I'm just using a scrap of aluminum as a turning fixture. The nose radius of the stop can be anything, it just makes tangent contact to the center plate. So by using 2 of the holes & sandwiching the plates together, it makes quick work of making the curve profile for both parts simultaneously. I hate interrupted cutting because hot chips have a way of finding my head, so I bandsawed most of it away beforehand.

 

[PeterT]

Here it is installed. Seems to work well. I'll blacken it next time I do a batch.
I wish I could think of something similar for the cross axis but its a bit more cumbersome. If you come across any ideas let me know.

 

[Janger]

Peter that's nice. I like it. Simple and elegant.

 

[RobinHood]

I wish I could think of something similar for the cross axis but its a bit more cumbersome. If you come across any ideas let me know.

Nice work Peter.

would you be using both X and Y axis stops at the same time? Could you mount your vice 90* from the usual position (inline with the x-axis ) and use the stops you just made?

 

[PeterT]

Thanks John. It looks better in black now that its done, but almost impossible to make out any details photo wise so figured I'd take a few pics in the bare. I know you & I have discussed blackening so passing on - I had the dreaded WTF blackening the main center piece. All blotchy & weird rainbows. The other pieces turned out great so not sure what goes on there when it happens. I have sticks of regular 1018 I got from OLM & for some reason they take the black excellent. I'm starting to think less to do with the surface prep since that was identical & squeaky clean. Something to do with the metal itself. It was a bar of CRS I've had laying around. But it had 0.010-0.015 skim passes off each face so should have been good metal. It improved with a couple of extra re-do's trying steel wool & scotch brite... about the only thing that helped was fresh blackening. Then to cap it off I realized I was going to round over the upper corners & forgot that too. I wish stainless wasn't so expensive (like 3x regualar 1018) or I'd use it more.

Rudy, kind of depends on the part application. The valve cover is a good example. First op is a rouging slot that is only X back & forth between 2 stops (left sketch on the diagram). For this part it removes most of the material & is a necessary part feature anyways. Then the second op is rectangular coordinate pocket that would be both X & Y movement around the periphery all in one vise setup. You can see on right sketch where I superimpose end mill diameter & that gives me corner coordinates (+/- actual end mill diameter). What I've found, at least on aluminum with sharp end mills & reasonable depth/diameter cuts, is if I can rough enough material so the final side milling doesn't have a lot of net material to remove (say 0.010-0.020") , I can just plunge straight into each of the corner coordinates & then basically make one continuous finishing pass at depth around the inside. So just one time 'reading the numbers'. Another method is driving into each of the corners. But I find it inevitably chatters or drifts a bit because EM is loaded differently. I've seen people do pocketing different ways but the question is always what kind of tolerance are they holding, surface finish, material... etc. My width has to be within a thou or so. So if I had similar stops in Y direction it would be just a bit easier. Just set them up & go corner to corner & gradually work my way to depth. That would also allow one EM in most cases. Hope I interpreted your question correctly.

I find the biggest headache in pocketing is vacating chips each pass because if you don't get them out, they get munched up & re-ground & make a mess of the part & gall up the cutter. I don't like even soft compressed air because the swarf from high helix EMs are like daggers - sharp & dangerous enough just lying around never mind going through the air. So I just put the shop vac nozzle & suck them out as necessary. PITA but much safer. In an industrial setting I guess that's why they turn the coolant on fire hydrant mode LOL.

 

[RobinHood]

Yup, you got what is was asking. I forgot that you are making multiple parts with the same dimensions (in this case pockets). It does make a lot of sense to take the time once to set-up your stops.
My Bridgeport came with adjustable solid stops; also x axis feed stops. I have not yet checked repeatability. I do use the stops on occasion. No provision for y stops from factory.

 

[PeterT]

I made this Y stop contraption for my RF45. I was kind of reluctant to drill holes experimenting so I borrowed one of the 2 bolt holes used to mount the leadscrew front casting plate. Basically spacer, a vertical bar & threaded rod with nuts on either side to set the stop position. It worked but... so-so. Too much flex. A stop needs to be beefy and/or clamped secure. Mind you, if its just for mindless roughing you can set it 20 thou away & its ok if it drifts a bit as you progress. But it might be just as easy to set a dial up on a mag arm. None of this is worth the bother on a couple parts. Its when you have a dozen to make & the tolerances are more stringent.