New Mill

[david pierce]

Tom,
Take a look at item 230927637750 on Ebay. It does not offer dividing plates but for divisions that will divide evenly into 360 it will function well. If you need to you can pick up a 4″ table with dividing plates in the future.
david

[tmac1956]

david:

That is much cheaper than what I was looking at – and you’re right about the later upgrade. I’m probably a ways off from being able to use index plates anyway.

I’ll book mark that one.

Thanks!
Tom

[david pierce]

Tom,
In general the holes work out better for indexing and the degree markings work out better for angles. They can however cross over and if you are careful to line up your marks, you can get fairly accurate indexing with that unit. The gear ratio between the worm and worm gear reduces the error in the hole plate or mark by that ratio. For example, the 3″ unit I listed has a 36:1 ratio and any inaccuracy in lining up your marks will be reduced by that amount. The least accurate method is to use a direct hole plate as any inaccuracy in the holes will directly transfer to the part.
david

[tmac1956]

david:

I appreciate the information. As always – thank you!!!

Tom

[tmac1956]

David:

I found two Youtube videos showing three methods (two manual methods) for locating holes. I just thought I would pass them along. Since I don’t have DRO’s, it looks like I need to get a height gage. This guy is pretty good – you can tell he’s spent alot of time teaching too.

http://www.youtube.com/watch?v=t6evpRPPlrY

Thanks!
Tom

[david pierce]

Tom,
There are a few things to consider after watching this video. First, is the degree of precision desired going to be obtained using these methods? If the answer is yes than go with the easiest method. If the answer is no than these methods will probably not apply. There are a few other things I would do differently. One is I prefer the Kurt design ball lock vice to the old Bridgeport vice in the video. The Kurt design is the vice you currently have. I also like to use a lubricant when cutting anything (with the exception of cast iron where you would use an air blast). My personal lubricant of choice is inexpensive motor oil that I apply to the part and cutter with a cheap small paint brush. As far as a readout goes, I am almost certain that one can be purchased comerically for your mill. When I was a machinist, we had a DRO on every machine in the shop. They can be a great timesaver but they are not a magic bullet to produce high precision work. Mounting either dial or analog dial indicators to your mill axies will provide precision positioning at a lower cost.
david

[tmac1956]

david:

I’ll probably stay with the analog dials for now as I need other things more than the DRO’s. I probably need to learn the fundamentals of aligning workpoints manually anyway first.

Thanks again!
Tom

[david pierce]

Tom,
Something I forgot to mention. When I use a reamer I slow the spindle way down and use plenty of oil.
david

[arutha]

David, a quick question if I may?
I used to work in an engineering factory years ago and we used to use prarafin on the taps to aid cutting and clearing swarf, is this something you are familiar with?
I have a cutting oil which I use mostly on steel parts but I have often wondered if you can get away with using any oil, I know it is supposed to help the cutter “bite” and also to help cool the material and bit when cutting?
Paul.

[david pierce]

Paul,
Any cutting action is a resust of force applied against something to be cut. The principal works on pressure over area. This means that the smaller the area the greater the force. When a tap cuts out a thread or a graver or cutting tool peals off a chip, the metal is actually being ripped away. This is why a nice shinny watch pivot looks like a mountain range under magnafication. The purpose of a lubricant is to reduce the friction between the moving surfaces and tear the metal away in a more controlled manner. If you take oil and lower the temperature it will turn into a solid just like parafin. Parifin just happens to be in a solid form at normal temperature. It is in fact an oil and due to its lower cost is the fuel of choice for large ships. It is simply heated up and pumped into the cylinders as a liquid. It does have lubricity in its natural solid form but when heated by the friction of the cutter movement it turns into a liquid and provides more coverage between the moving parts. As far as which oil to use, companies have spent a lot of time and money on research on which combination of chemicals work best on which materials in different situations. When something is especially formulated to tap steel or aluminum or titanium or various other metals it is due to the fact that companies have had problems with tap breakage or nasty looking threads. I have found that oil works well in most situations and does not cost a lot so I use it. If I have problems with the process then I will look for other and usually more expensive solutions. When you buy a can of cutting oil it will have a mix of other things in the oil such as sulfur to make it work a little better than the cheap stuff that I normally use.
david

[tmac1956]

@david pierce wrote:

Tom,
Something I forgot to mention. When I use a reamer I slow the spindle way down and use plenty of oil.
david

David:

I understand you’re not supposed to run them backwards either.

Thanks!
Tom

[david pierce]

Tom,
That is true. Also, a reamer should only remove a couple of thousandths of metal. Its purpose is only to size the hole but many people try to use a reamer as the final drill size; bad idea! I like to drill first up to about .015 inches under, then use a boreing bar to get the hole to within a few thousandths undersize, then use the reamer for the final size. For a hole requiring extreme precision such as a valve guide that must prevent oil leakage or an ejector pin on a plastic injection mold, the hole would be reamed slightly undersize (.0001) and then lapped or honed with a SUNNIN HONING MACHINE.
david

[tmac1956]

@david pierce wrote:

Tom,
That is true. Also, a reamer should only remove a couple of thousandths of metal. Its purpose is only to size the hole but many people try to use a reamer as the final drill size; bad idea! I like to drill first up to about .015 inches under, then use a boreing bar to get the hole to within a few thousandths undersize, then use the reamer for the final size. For a hole requiring extreme precision such as a valve guide that must prevent oil leakage or an ejector pin on a plastic injection mold, the hole would be reamed slightly undersize (.0001) and then lapped or honed with a SUNNIN HONING MACHINE.
david

david:

I’ve only used a reamer once so far and that was to create a bushing for my QC tool post bolt to get rid of the wobble from using a smaller bolt than the one it’s set up to accept. I used a standard reaming chart for this, but started out with a center drill, then drilled a pilot hole, then a slightly under-sized drill, and then finally reamed it out to size. The bolt was a tight press fit into the bushing, so everything seemed to work out well. I’ll be sure to keep the above in mind in the future.

Thanks!
tm

[david pierce]

Tom,
Like many things machining is learned through study and practice. When I started back in the mid 1970s it was a transitional period from the old school tool and die makers and their “by gosh and by golly” methods of making parts, to a system of machining to mathematical models. Under the old system no two parts were ever the same and everything was hand fit to make it work in conjunction with other parts. If you go to Youtube and watch the way watch parts are actually made in modern watch factories, you will see that even the watch industry has switched to this paradigm. There are several good reference sources that should be studied such as used school textbooks from machine shop classes and the machinist handbook. The books are expensive new but you can probably find less expensive used copies from ebay and other used book stores such as Amazon.
david

[tmac1956]

david:

I have the machinist handbook. It looks alot like the strutural steel handbooks that used in the structural engineering industry when we sized structural members. It also contained standard data for designing connections, bolts, plates, channels. math formulas, etc. I can see a parallel between the industry I was in for about twenty years where we went from hand calculations to using 3D integrated finite analysis software for design and in some areas of the industry, for fabrication.

Oh… I do have another question. When I attach my 3-way cross slide to my lathe and mount my QC tool post with a 1/4″ cutting tool in places, I have to push the tool all the way to bottom of the holder. When I do this, it’s just a few thousands above the centerline of the lathe head stock. This leads me to see the need to take a few thousands off of the bottom of the alluminum tool holder. Any thoughs on this?

Thanks!
Tom

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