milling underframes

[dmdmn]

i want to put athearn genesis ge hi ad trucks on my intermountain gevo locomotives.  the genesis gearbox tower is further towards the ends of the unit so some material needs to be removed from the intermountain underframe. i have a taig lathe and milling attachments. could anyone help me out and tell me the best way to do this, like what kind of bits i need? there is very little information on how to use these machines anywhere. any machinists on here?

[slowfreight]

Can you upload photos? Lacking much for machine tools myself, I've done a lot with hack saw and file. I found it worked better than Dremel because the material is soft and tends to clog grinding tools.

[dmdmn]

no i cant upload photos, i have the milling attachment for the taig lathe. i am kind of thinking i need side cutting reamer bits instead of end mills. this machining and milling thing seems like a real uphill battle as noone can give any information.

[big train james]

I'm fairly new to machining, but I'll take a shot at this. I'm going to make some presumptions about how and what you need to cut, if I'm off base let me know and we will reconsider things.

I'm presuming:
you are cutting a diecast frame, so a fairly soft metal,
and that you aren't cutting anything particularly complicated, mostly just removing material,
and that tolerances probably aren't that critical.

I'm also presuming that since you are using a Taig setup, that you are using ER25 collets, with a max diameter of 3/8".

So if you are just removing material, effectively either a facing cut from the top down, or a contour cut from the side, I would go with a high speed steel end mill. I would use the largest diameter standard size that you can fit in your mill, which would be 3/8", but which will also fit between any features on the existing frame which need to remain.

If you need to cut a slot, then it would be best to use a center cut flat end mill. It's designed to cut on the end of the cutter as well as the sides, whereas a regular flat end mill isn't really intended to cut with the end of the bit so much. The difference would come into play if you need to plunge straight into the work piece, like for entry into a slot operation. You could get away with a regular flat end mill here though, because the frame material is pretty soft. Also, using light cuts will ease the burden on the cutter.

For cutter diameter, you could use one equal to the width of the slot. This is the simplest solution, and it will probably work fine in this case because the metal is soft and finish isn't super critical. Ideally however, it would be better to use a cutter incrementally smaller in diameter than the width of the slot, as cutting each side of the slot individually will yield a better finish (otherwise one side is climb milling and the other is conventional milling). But it's probably not necessary in this case.

And lastly, if you are cutting a pocket, then use the biggest diameter flat end mill that fits inside the pocket, but also is incrementally smaller in radius than the smallest corner radius.

This would be the time to think ahead a bit and consider what other machine work you might take on, in the sense that you can buy the best cutter for this job only, or you could possibly go for something with a broader spec so that the cutter is more versatile. But here are some things to consider.

Regular flat end mills in HSS are probably the most affordable cutters you will be able to get. A quick check of the Google says +/-$10 for a 3/8" mill.

You almost certainly don't need a reamer for this operation, in fact I wouldn't use a reamer unless I needed a very accurate hole.

I would go with a 2 flute cutter for softer materials, including plastic, diecast, brass, and aluminum. It will help with clearing chips, which is better for the tool, the part, and the quality of the cut.

Cutters will have an overall length, but only part of that length will be sharpened with flutes (the cutting length). It is generally better to use a cutter with the shortest necessary cutting length to perform the desired operation, as the cutter will be stronger than one with a longer cutting length. They will often be cheaper as well, since they are easier to make. It probably doesn't matter too much at the sizes we are dealing with in model railroading, because the total depth of cuts, holes, or pockets is fairly limited. I'd probably look for something between 1/2" and 1" cutting length.

Speeds and feeds will depend on what material you are cutting and what diameter cutter you choose. There are plenty of apps online that calculate speeds and feeds once you populate various criteria fields. Also, a cutter manufacturer will usually provide speed and feed specs for their cutters, so you might be able to work just from that.

Fortunately, soft materials are pretty forgiving with respect to breaking cutters. However, I would use caution if you go to 1/8" or smaller cutters, with respect to feed rate. 3/8" or 1/4" cutters are fairly robust, but the smaller cutters just don't have as much meat in them to survive rough handling. Just like bits for pin vises, breaking and replacing them over and over gets old pretty quickly.

That should get you started. Let me know if there are different parameters for the job, but I think this will cover a lot of what you might need to do.

Here's the obligatory safety push, wear safety glasses, keep your fingers and everything else out of the machine, and make sure you secure your work piece properly. Don't half-ass anything.

Jim

[dmdmn]

thanks so much! i have the taig 1040 collet set and the 3/16 end mills, with the collet set the biggest i can go is 1/4 inch. i just have to take .156 off the ends where the trucks go in as the athearn gearbox is .156 closer to the ends of the frame and possibly shave some from the bottom of the bolsters. the er-25 requires a whole new headstock and costs about 500.00 us, so not an option for me. would the 1/4 inch centercut flat end mills work? i can take lighter cuts until i am through.

[big train james]

If you already have a 3/16" flat end mill, you could just proceed with that. However, moving up to the 1/4" end mill is also perfectly fine. It's a good excuse to buy some more cool tooling! 

The decision between regular end mill and center cutting probably comes down to cost difference.  It may be a moot point anyway, I'm kind of under the impression that most end mills offered these days are center cutting anyway, but that may be a carbide thing or just a machine shop practicality.  But if there isn't much difference in cost, I would just go with a center cutting flat end mill.  

The center cutting mill is better for plunge cuts, but the reality is that best practices can greatly reduce or even eliminate the need for such cuts.  Whenever possible, I would bring the tool to the proper depth off the part, and then move sideways into the work piece.  That way I'm not plunging into the work piece material directly, and I won't have a bad crash if the feed rate is too high or I misjudge the distance.  If I don't have a choice but to bring the cutter down into the part, for a pocket or a slot, I would still try to use a ramping motion (or helix if you have CNC) to achieve the depth of cut.  The net result is that I would expect to use straight plunge cuts into a part only when dealing with round holes and manual machine operation (as opposed to CNC).  Even then, I would almost certainly drill most of the material out first, and then finish the hole with an end mill or reamer.  Or if the tolerances were loose enough, I'd would just use a screw machine length drill bit that matched the desired hole diameter.  Screw machine bits are shorter in length than regular jobber bits, and are therefore typically more stout and result in more precise holes.

There is a Taig CNC mill in my somewhat immediate future.  I was surprised that such capability was available for a lot less money than I expected.  I've been taking machining classes at the local community college for a year or so, and most recently started in with manual CNC programming as well as Mastercam CNC programming.  I've been doing 3d cad work even before that, and I have lots of model things that I've drawn and I'd like to cut, so I'm pretty excited about the prospect.  The Taig isn't going to do much heavy work, but that's limited in the modeling environment anyway.  Down the road I might try to score a more serious mill, but that will require the right combination of luck, money, space, and need.

By the way, there are a couple of good home machinists forums around online, and there are plenty of modelers on them.  I'll see if I can dig up the links.

Jim

[dmdmn]

so you are saying that the end mills can be used like a reamer? can you make a slot and go right through with the end mills? maybe i could drill holes with a drill press and just mill the leftover material out.

[big train james]

Is the reamer question a general thing, or specific to what you want to do with this frame? I can't imagine anything you are proposing to do to the frame that would warrant using a reamer.

That being said, I guess I'd probably say that an end mill could be used like a drill bit, rather than a reamer*. Drill bits and end mills are mostly about removing material, to a certain tolerance. Reamers are pretty specific tools for finishing holes to a tight tolerance, I would only use one if I needed a very specific hole size, finish, or roundness. And I would only ever use it to remove the last bit of material from the sides of the hole, having done the brunt of the work with a suitable drill bit. Could you do these things with an end mill? Sure, but not to the same degree as with a reamer.

You could effectively drill (or counterbore) a hole with an end mill, depending on material, and you could effectively bring a hole to size with an end mill, but a drill would probably be better for material removal, and a reamer would be better for finish and precision. Of course, if you need a flat bottomed hole of a specific depth, you can't use a drill for that.  

Regarding making a slot and going right through, I presume you mean the slot is cut all the way through the work piece as opposed to being blind? If so, then yes, you can do that with your end mill. Especially a center cutting mill. They are also known as slot mills, because that's what they are intended to cut, and plunging is pretty common when cutting slots. Going part way through or going all the way through makes no difference, other than the number of cuts you have to take to finish the cut. But you can also do this with a regular end mill. If you do need to cut a slot, I wouldn't bother with drilling and then milling the remainder. I would use the appropriate end mill and do the job with a single tool and a single setup.

* There are lots of rules of thumb in machining, and there are lots of optimal tools and techniques when in a perfect world. But everything is conditional, pending material to be cut, available cutters, tolerances, budget, time, skill, design intent, and of course the machine itself.

Here are a couple of links that discuss plunging with regular end mills, and the difference between end mills and slot mills.  I see mentioned in one of the discussions that many end mills are now made with the cutting edges on the end similar to a slot drill, which is what I mentioned earlier.  

Practical Machinist
Home Shop Machinist
Mig-welding UK

There is a lot of chatter about entry helix and ramp cuts, associated with CNC, but the general info about the cutters is the important part.

[dmdmn]

very informative, thanks again!! i just need to remove .156 of material on each end where the truck gear tower comes through the frame. the genesis gear tower is .156 closer to the ends than the intermountain gear tower. do you thing the taig milling bits are sufficient? or should i look around for different ones.

[big train james]

I don't have any experience with the Taig cutters. I just took a look on their website, which reminds me about one of my beefs with them. They really don't do a very good job of describing their products in any kind of detail.

Anyhoo, the Taig cutters should work for this task, I would think. Since you have them in hand, I would go ahead and try the largest diameter cutter. I would prefer a 2-flute cutter for the reasons described previously, but take a shot with the Taig first. Just check periodically to make sure that you aren't clogging the flutes with chips.

One other thing to consider is the cutting length. It doesn't look very long, so make sure that you keep the cutting portion of the tool at the correct depth. This is what I mean about the website. I have no idea how long the cutter is overall, and I have no idea about the length of the cutting edges. It would also be useful to know what material the cutter is made from.

I would take the tool to depth off the part, inside the hole for the gear tower. Then move horizontally to the end of the gear tower opening. With appropriate feed and speed, I doubt you'll have any issues with this operation utilizing the Taig cutter.

[dmdmn]

thats what i found with taig as well. very little information. i see amazon has all kinds of milling bits, could you check and see which one would be right for what i want to do? i should probably take a scrap underframe and experiment to get a feel for what the machine will do.

[big train james]

I would start with the end mills that you already have in hand, before buying anything else.

It's a very prudent idea to test the tool on some scrap. This should give you an idea of how the tool behaves and how effective it is, and you could also make sure that speeds and feeds work as planned. Again, I would chuck up one of your Taig cutters and have a go.

I don't really expect Taig to explain to me how to use their machine tools, but I would like them to offer better descriptions for the products they offer. The specs for the cutters are one thing, it's another to not thoroughly explain the difference between the various mills or lathes that are offered. I can see that they have different prices, but not much more than that.

There are resources available under the resource tab, with links to user forums or specific user sites. I would take a look at some of those sites. I would also suggest that you join one or both of the forums linked to above, and start asking questions there. I'm pretty much at the limit of my knowledge at this point, I've learned a fair amount but it's almost all theoretical. The people on the home machinist type forums have real empirical knowledge, and they will be able to answer more specific questions for you, like what type of cutters to recommend.

I've never bought any end mills or any other tooling, so any guess as to what to buy from Amazon would be a shot in the dark. That being said, here are some links that would seem to be in the vein of what you might use:

Speed Tiger
SpeToollink
CGC Tools

There are issues or questions, of course.  One is only available as a set of 5 cutters.  They aren't expensive per each, but 5 cutters will lastyou a long time if you use them correctly.  I think they all carbide, and at least one is coated.  Normally, carbide would be overkill for cutting softer materials.  But is it problematic to use carbide for aluminum or brass?  The same applies to coatings.  These are the types of questions that I don't have the answers to, but you could almost certainly get answered via one of the home machinist forums.

I also suspect that there must be cheaper cutters somewhere on Amazon, but I didn't stumble onto anything obvious.  A lot of stuff is geared toward CNC, and a lot of the tooling is carbide.  Both are practical realities of modern machining.  But there has to be some HSS out there somewhere.  One other problem is that a lot of the sets of cheaper mills include sizes that you cannot use, meaning they exceed the size of the collets you can use.

Is there any chance that you have a tool and supply type shop local to you?  They would be a good resource to ask what you need for the work you want to perform, and usually have options for tooling at various price points.

[dmdmn]

i tried milling out the underframe with my end mills and it was a disaster, i could probably do a better job with my dremel. i think the reamer would be the better choice as all i am doing is enlarging the hole that is already there. what i am trying to do is make the athearn genesis ge hiad trucks on the intermountain underframe. the genesis gear tower is further towards the end of the frame by about .156 so that amount of material needs to be removed, also it looks like i will have to shave about .020 from the bottom of the bolsters as the genesis trucks are higher where they mount. maybe it would be just as good if i sscratchbuild a whole new underframe from brass shapes. i have to do this someway as i never liked the trucks on the intermountain gevo.

[big train james]

That's unfortunate. What exactly happened that made it a disaster? I'm sure that you could accomplish the work with hand tools or a dremel, as you mention. But it would be nice to put the mill and lathe tools to work.

[dmdmn]

i revisited things today and it turns out i wasnt running my spindle fast enough, i shaved the bolsters down today and the end mills worked beautifully!! it would be good to get some bigger ones though. i guess i was expecting too much being the first time i ever tried this. i can repair the underframe with jb weld to make things look neater and remill.

[big train james]

Excellent! I'm glad to hear that things improved on the second attempt.

I was going to guess feed rate or spindle speed were the possible culprits, absent any other obvious issues. The best part is that you now have a successful operation under your belt.

[dmdmn]

is there a such thing as a depth stop for the cross slide? the carriage has a depth stop. a depth stop for the cross slide would be very useful as then i could never go to far in either direction.

[icghogger]

Not sure about the Taig, but there carriage micrometer stops for small lathers that attach to the ways. Most are after-market attachments. Before I bought one for my Unimat, I used masking tape across the ways.

[big train james]

Never heard of a stop for the cross slide, just the carriage type. That doesn't mean they don't exist, you would need to start looking around on the net. Or ask on one of the machining forums.