Thread: Spotfacing an odd size on a milling machine

I have to create a 1 5/8" diameter spotface using a milling machine, but don't want to buy a dedicated spotfacing tool just for the one hole I have to make. What are my alternatives? I'm thinking that a flycutter with the appropriate bit would work, but I'd like to know if anyone has any experience with this because I'm working on a cast iron casting and only have one shot at getting it right, or I have to buy a new casting. The spotface will be used as a sealing joint and not just to even our the load of a bolt.

Thanks,
Dorsey

Have you a facing head for the mill?

Any chance of getting the part in a lathe?

Put it on a rotab on the mill ?

The mill is in a Vo-Tech which doesn't have a large selection of tooling and no rotary table. I can't use a lathe because I only have a three-jaw chuck and thus no way to hold or accurately position the casting.

Why not use a boring head with a somewhat small, but flat bottomed, toolbit to make the OD of the spot face to size and depth. Then follow up with a smaller (i.e. 1/2" or so) end mill and just mill out inside the outer ring you first made with the boring head?

That's a good idea. I had thought about using a boring head to get the O.D. correct, but not using a smaller diameter end mill to clean it up. I think that there's a 1 1/4" end mill in the school's tool crib, so that should work, even if I can't get perfect results.

Originally Posted by Dorsey

That's a good idea. I had thought about using a boring head to get the O.D. correct, but not using a smaller diameter end mill to clean it up. I think that there's a 1 1/4" end mill in the school's tool crib, so that should work, even if I can't get perfect results.

The end of an end mill is not flat, so a plunge cut will not create a flat surface.

Larry

Does the spotface necessarily have to be round? As Larry said, the end of an endmill isn't flat, and, on a typical knee mill, an endmill that big will likely chatter regardless of whether its end is flat or relieved. IOW, can you take say a 1/2" endmill and create your spotface as a square with rounded corners? The finish will be better and the surface will be flat.

Yes, it does have to be both round and flat. The reason I'm asking for an alternative to a spotface cutter is because of the cutter cost exceeds the value of the part, so that's not an option for me. Same with the cost of a large end mill, flat bottom or otherwise.

One other thought --- don't overlook DRO functions if you have a DRO. There's more in there than just coordinate positions. Most will have an NC type function that manually lets you manipulate the two axis to follow a programmed shape. Every DRO should have a bolt hole pattern program. Just load a bunch of holes into the program and you'll get a similar effect. Be sure to factor in the diameter of the end mill you are using, though, and reduce the BCD accordingly. The spot face won't be perfect, but should be 99% there. Then just make a light finishing cut with a boring head to clear up the ridges left from manually going around.

Originally Posted by Dorsey

Yes, it does have to be both round and flat. The reason I'm asking for an alternative to a spotface cutter is because of the cutter cost exceeds the value of the part, so that's not an option for me. Same with the cost of a large end mill, flat bottom or otherwise.

You are in school, so this is a "moonlight" job, eh?

Refuse the job, the risk is too high. Or the "customer" can supply the tooling.

If the customer could supply a 1 5/8 twist drill, the point could be ground flat.

When you are done, restore the point of the twist drill.

I'm an adult evening student at the vo-tech and also the customer. I've overcome many challenges caused by lack of my experience, zero assistance, and the age and sorry condition of the equipment. Had I known that this project required this particular feature, I would likely have chosen a different project.

To be fair to the school, the 14" South Bend lathe and Bridgeport-type vertical milling machine I use are in their welding shop, and I have a special arrangement with the welding instructor (a personal friend) that allows me to use the school's equipment about 50 hours per year. As you might expect, I have to plan my time very carefully to maximize the amount of work I can accomplish. For example, I can't switch from a three-jaw to a four-jaw chuck because by the time I did so, my evening time would be up and I have to leave the tools the way I find them. The threading dial has been broken in the 20 years I've been going there and will never be repaired because the lathe is not fundamental to the school's welding program. Similarly with the milling machine - I can't disturb tram (although I do check it periodically) or switch out the vice for the same reason. Thus, all of my operations have to be fairly simple and straightforward within the limits of what I have available. Beggars can't be choosers.

There may be a 1 5/8" twist drill in the tool crib, now that you mention it.

You'll probably find a flat bottomed drill of 1-5/8" dia will chatter around also. How deep can the spot-face be ? Regards Tyrone.

Originally Posted by Tyrone Shoelaces

You'll probably find a flat bottomed drill of 1-5/8" dia will chatter around also. How deep can the spot-face be ? Regards Tyrone.

Sometimes, the only option is spending money on something.

Round Bar, Set Screw and Broken Center drill.

Turn round bar to fit biggest collet.
Turn round bar for snug fit in hole to be spot faced - no slop but "turnable" helps hold down chatter.
Drill round bar for center drill (a hole ninety degrees to round bar axis).
Drill and tap round bar for set screw to secure center drill - grind a flat on it for this purpose.
Grind center drill to do the cutting wanted - especially the flat part ninety degrees to spindle axis - you could even have a nice little corner radius if wanted.

Now you have a freebie piloted 1 5/8 spot face.

Machine MUST run super slow - even if you have to turn spindle with a wrench on the draw bar and finish with super light scraping cuts.

how big is the thru hole
get a boring bar in that hole as a guide
grind a hispeed tool so you get a flat bottom
and backfeed it
if its a goofy size hole make a bushing to fit hole and bar

Johnoder's homemade spotface tool is the way I do it, except I usually use a piece of 3/16" HSS tool bit

Originally Posted by Dorsey

For example, I can't switch from a three-jaw to a four-jaw chuck because by the time I did so, my evening time would be up and I have to leave the tools the way I find them. Similarly with the milling machine - I can't disturb tram (although I do check it periodically) or switch out the vice for the same reason. Thus, all of my operations have to be fairly simple and straightforward within the limits of what I have available.

i understand your position but it really only takes a few minutes to switch out a lathe chuck or tram a bridgeport style mill head.
maybe your time would be well spent just practicing getting those operations down to a few minutes each so your not limited by tram and or chuck size.
then perhaps a faceplate, some creative workholding solutions and a boring bar on the lathe with a custom grind would be a good option.

That "special arrangement" doesn't sound so special, and I wonder if it's because you've been going there and using the machines (for free?) for twenty years and you have never fixed that threading dial as a show of gratitude.

Threading dials have been made out of blocks of wood, dials of wood, and gears of wood. It's a lightly stressed component that doesn't demand much in the way of exactitude.


When I borrow something, when I rent something, if an opportunity arises to leave it in better shape than what I found, I take that opportunity.

I recently sold a Makita cordless drill to a buddy. It had two batteries, one charger; "All There".

Last week I was walking through the debris field of shop that was being cleaned out, I asked for two orphaned chargers and battery lying on the floor. Buddy now has three chargers, and three batteries; my cost was the effort of asking for them.

Over the course of twenty years, you could have / should have built up some goodwill, so when you bump up against a situation like the one you have, you might not have to be asking strangers for help.

Just the way I see it, and I know it's a bit harsh.

Steve

that's not 'harsh' at all, its called giving more than you take and its a lost art.
(not implying anything about you OP)

I have plenty of good will built up over that period of time, not that it's anyone's business but mine. The reason I can't ask for help is that the school shut down their machine shop program 15 years ago due to lack of interest and the welding instructor knows less than I do (which isn't much). My day job is Chief Technology Officer at an internet company so there's no one to ask there, either; few in my organization even know what a milling machine is. Not that that's anyone's business, either.

Please stick to relevant answers and avoid sermonizing or going off-topic with irrelevant (and uninteresting) personal stories that are not germane to the thread. I'm asking for help and advice on a specific problem from a group whose opinions I respect in a specific area, not life advice from strangers.

I think that I've gotten some good advice and am now closing my interest in this thread. Thanks for all of you who offered genuine help and no thanks to the others.