Author Topic: Machining a flat face with good surface finish and accuracy  (Read 3934 times)

Offline picclock

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Hi
Bit of an odd question. I have recently had to make a steel plate which had to be flat and have a very fine surface finish (basically mirror). I really struggled with this so it would be useful to know if there was a better solution out there.

I tried fly cutting, but found I could get better results by using an endmill with multiple passes. After that I attached wet and dry paper to an MT2 blank I had which was wider than the part with double sided sticky tape and moved the work under it on the mill whilst it was rotating at low speed. After replacing the paper half a dozen times, and checking it was still flat, the job was done.

I don't have room (or funds) for a surface grinder, but I had thoughts about getting hold of a silicon carbide wheel and fitting it to the mill - somehow - to see if it could work be a poor mans surface grinder. 

Any other ideas most welcome

Best Regards

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline ieezitin

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Re: Machining a flat face with good surface finish and accuracy
« Reply #1 on: July 10, 2016, 08:05:34 AM »
Try a shear tool in the fly cutter. Do you have a shaper?

Anthony.
If you cant fix it, get another hobby.

Offline Pete.

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Re: Machining a flat face with good surface finish and accuracy
« Reply #2 on: July 10, 2016, 08:40:17 AM »
Buy and old cast iron surface plate and some diamond lapping paste.

Offline PekkaNF

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Re: Machining a flat face with good surface finish and accuracy
« Reply #3 on: July 10, 2016, 10:31:38 AM »
I would not use abrassives on mill for two reasons: wear and it actually does not increase accuracy.

Surface grinders are next logical step from the mill, but to produce more flat, they are different machine, more accurate way geometry and more accurate spindle, but less load carrying capacity on other directions. Therefore surface grinder attachemets on the mill are usually used when material it too hard to mill, not much extra accuracy is gained.

Your observation on fly cutter vs. end mill is correct. Tramming affects less on cutters of smaller diameter.

You need to define how flat you need that piece first. Here you might resort to scraping, least you need to check it with blue.

Abrassives will then even out surface quality, but will not improve much flatness, easily decrease it actually, specially on the edges.

Lapping on cast iron plate is probably easiest and cheapest - specially if you do have the cast iron plate.

Pekka

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #4 on: July 10, 2016, 10:47:35 AM »
I use a 80mm cone grinding wheel in a home made arbor , gets a good finnish needs a realy fine down feed is needed  to mutch and the stone cloges up , cover up well and vacume at the end of the job no problems so far .
Jeff

Offline RobWilson

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Re: Machining a flat face with good surface finish and accuracy
« Reply #5 on: July 10, 2016, 11:40:38 AM »
Hi I really struggled with this so it would be useful to know if there was a better solution out there.


There is , get someone else to do all the hard work  :med:         I use this supplier   http://www.groundflatstock.com/Shop/CategoryID/1/ProductID/3  , price is per 500mm  ,



Rob

Offline hanermo

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Re: Machining a flat face with good surface finish and accuracy
« Reply #6 on: July 10, 2016, 01:48:07 PM »
Unusually, disagree with PekkaF.

Abrasives will average local surface errors, thus making stuff more consistent.
Mostly avoiding edges, this will make the object more flat.

Even some modern toolmakers use abrasives to make tools for Haas, in their haas mills, with grinding stones.
Fwiw.
Youtube.

Offline picclock

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Re: Machining a flat face with good surface finish and accuracy
« Reply #7 on: July 11, 2016, 02:22:17 AM »
Hi, Thanks for your interest and replies.

No shaper, no cast iron plate. As a side issue, what happens when the cast iron plate becomes abraded and no longer flat  :scratch:

@PekkaF - The nub of the problem is that you can machine a surface flat overall but the machining marks make it a poor surface. So to get a good surface its necessary to abrade it up to the depth of the machining marks, and in doing so some of the cutting accuracy is lost. Hence my thought that an abrasive wheel on the mill may be an option to get the finish and maintain the accuracy.

@chipenter - Sounds like you have been there and done it. Was it a silicon carbide cone? What sort of speeds did you use? Any chance of a picture ?

@hanermo - Looked up some links on you tube and was quite surprised to see them using grinding stones on a mill. Should have done that before. Seems like its an acceptable solution.

Many Thanks

Best regards

picclock

Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #8 on: July 11, 2016, 02:54:45 AM »
I will be using my gringing wheel later today ,  to finish 4 tool holders made from fork lift tines , this is tough stuff and hard to get a finnish on will take some photoes .
Jeff

Offline RobWilson

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Re: Machining a flat face with good surface finish and accuracy
« Reply #9 on: July 11, 2016, 10:40:19 AM »
Hi Picclock


How big is the job ?  I use a fly cutter  on large ish   jobs and get canny results .







I will be using my gringing wheel later today ,  to finish 4 tool holders made from fork lift tines , this is tough stuff and hard to get a finnish on will take some photoes .


Odd Jeff  I get a cracking finish on FLT fork material , machines a dream . ( I have access to and have tones of the stuff ) 








All above are just a few of the things I made from






Rob






 

Offline Joules

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Re: Machining a flat face with good surface finish and accuracy
« Reply #10 on: July 11, 2016, 11:49:12 AM »
Oh bugger !!!!

           Wish my machining work looked like that, nice work Rob.   :bow:
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline Joules

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Re: Machining a flat face with good surface finish and accuracy
« Reply #11 on: July 11, 2016, 01:59:12 PM »
https://youtu.be/ATG_UYYfx7w

Some great lapping video's and ideas when you go looking.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #12 on: July 11, 2016, 03:04:47 PM »
Set up for grinding today pillow cases held on with magnets , before and after shots oil blacking will get rid of the shine , these bits of fork lift tines must be different to yours Rob drilling and tapping 8mm was a pain brand new taps to .
Jeff

Offline kayzed1

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Re: Machining a flat face with good surface finish and accuracy
« Reply #13 on: July 11, 2016, 04:26:56 PM »
Rob has THAT camera out again :clap:

Offline tom osselton

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Re: Machining a flat face with good surface finish and accuracy
« Reply #14 on: July 11, 2016, 07:09:41 PM »
I've never thought of grinding like that!

Offline picclock

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Re: Machining a flat face with good surface finish and accuracy
« Reply #15 on: July 12, 2016, 02:33:49 AM »
@ chipenter

Many thanks for the pictures  :beer:. That was exactly the sort of thing I had in mind. The machinability of the steel obviously plays a major part in the initial finish.  Its quite amazing the quantity of dust kicked up by the process. What sort of depth of cut were you setting - 1-2 thou? It looks from your picture that you are using a grey wheel - Aluminium oxide ??

I thought I might experiment a bit and try a green grit wheel as these are sometimes used for getting a high quality finish on steel.  I notice RDG do a range of cup wheels for about 12 delivered, though they don't give any info as to grit size. A CBN (cubic boron nitride ??) wheel can be had though I am not sure the extra price justifies it.

Best Regards

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #16 on: July 12, 2016, 03:18:45 AM »
picclock a green wheel is too soft I have tried one and the wear on the stone is to mutch for acuracy , 1 thou cuts max any more and to mutch heat is gererated and the stone clogs and will need dressing , the stone is from RDG picked up at Ali pally show this is the finest grit wheel I have , the harder the steel the better the finish free cutting mild steel clogs the stone fairly quickly , I run at 2200 rpm the fastest my machine will go , the magnets are handy for collecting the steel dust as this can do nearly as mutch damage to the machine as the grit clean up took less than 5 minuets .
Jeff

Offline picclock

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Re: Machining a flat face with good surface finish and accuracy
« Reply #17 on: July 12, 2016, 05:12:36 AM »
Hi Chipenter

I think I will go for one of the RDG ones as your results seem very good. They appear to do a 100mm one for the same cost so I may get that one.

Quite honestly my knowledge of grinding as a process is minimal, limited to sharpening/making lathe tools out of HSS with the std bench type grinder, though I do have a diamond dressing stone/bar.

The reason I considered at the green stone (silicon carbide) comes from here :-

https://www.georgiagrindingwheel.com/grindingwheels_basics.htm#faq10

"One interesting characteristic of silicon carbides is the effect they have on steels.  Due to the sharpness of these grits, one would think that they would be too aggressive and not provide a good finish.  In fact, on steels, silicon carbide is used as a sort of polishing/finishing grit.  It is used in tumbling processes as a surface finishing product."

Best Regards

picclock



Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline mcostello

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Re: Machining a flat face with good surface finish and accuracy
« Reply #18 on: July 12, 2016, 10:17:48 AM »
If anyone wants to try and get a better finish from their surface grinder they should find Stan Zinkovsky's video from BarZ Industrial about putting jewlers rouge on a grinding wheel.
High Speed steel in a Carbide world.

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #19 on: July 12, 2016, 02:30:17 PM »
Don't fprget the thick paper or thin cardboard washers .
Jeff

Offline Will_D

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Re: Machining a flat face with good surface finish and accuracy
« Reply #20 on: July 12, 2016, 05:57:33 PM »
If anyone wants to try and get a better finish from their surface grinder they should find Stan Zinkovsky's video from BarZ Industrial about putting jewlers rouge on a grinding wheel.
Here's the link:

https://www.youtube.com/watch?v=j9Nx1O7WpsU
Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline picclock

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Re: Machining a flat face with good surface finish and accuracy
« Reply #21 on: July 14, 2016, 03:08:57 AM »
@ chipenter
Ordered the 100mm one from RDG. Load spreading washers fairly essential with stone/metal interface. An easy way to make them is to use a  dome headed nut/ball bearing over a hole of the correct size in a metal plate. Just tap it with a hammer and voila :thumbup: the perfect hole, very handy for gaskets. The nut/ball bearing size should be larger than the hole ~ roughly twice the size of the hole but its not critical. e.g if you want to make a 6mm hole an M6 dome nut is the way to go - if you stick an old screw in it, its easier to hold and hit.   

Best Regards

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline chipenter

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Re: Machining a flat face with good surface finish and accuracy
« Reply #22 on: July 14, 2016, 03:57:15 AM »
I have a set of wad punches use end grain of a log .
Jeff