[Roadsidejobshop]

Hello,

I am building a cnc surface grinder (very light duty) that I can also use as a manual machine. The goal is to finish my parts which come off the cnc mill and maybe do some experimenting. The goal of the machine is to take light finising passes and to smooth out the machining marks on the parts. Taking off 1-3 thousanths(0.0254 to 0.0762mm) per pass is what I'm looking for .
I'm on a very strict budget and the machine frame is made from scrap material or material that I got for a very good price. After welding, I will also have it stress relieved (got a friend to do it).

X-AXIS

The X-axis is riding on MGN09 rails with MGN09CA carriages ( 6 of them). The rail length will total 990mm, the main mounting plate will be 1050x180x15mm, made from S355J steel.

Y-AXIS

The y-axis is riding on HGR15 rails with HGH15CA carriages (4 of them). The rail length will be 400mm. They will mount to the base frame.

Z-AXIS

The z-axis will be custom made and will essentially be a box-way(although very much flimsier compared to real ones). The z-axis spindle carriage will slide on a Teflon /PTFE surface, 2mm thick.

SCREWS

All screws are based on TR12x3, with anti-backlash nuts. Considering the light duty the machine is running I did not see it important to put ballscrews in there.

ELECTRONICS and MOTORS

Motors will be NEMA 23, probably 1.26 or 1.89NM ones, breakoutboard combatible with Mach 3.

I'll post more pictures and stuff when it comes available

[Roadsidejobshop]

Found some more pictures and a video too - beware, a lot of rambling



As you can see from the pictures, the design has changed quite a bit already.

[Roadsidejobshop]

Hello people, I've been working on the surface grinder and a bit more has been completed - the second video about the build is now ready and uploaded

[Roadsidejobshop]

Hello people - an update on the surface grinder build. I decided to tackle the biggest mill job first - since I'm only learning the machine and program (and the part was 2x the reach of the machine on the X axis). It turned out really nice and so far I''ve spent about 4-5 hours on the machining alone (i'm guessing another 3-4 to go). Enjoy the pictures - next video coming soon.
Thanks for reading

[Roadsidejobshop]

More updates - things are moving along, although they are taking longer than expected. I'll try to post more updates soon

[DSpeck]

Interesting build - don't see many people here making surface grinders! Best of luck with your build.

I hope you have made provision to cover your rails thoroughly - grit getting on them will make them wear out very quickly, otherwise. We use surface grinders at work, and they are messy tools - lubricant mist mixed with abrasive from the wheels and very fine grindings from the part make an abrasive mud. You will also need to design a coolant return/filter.

Another concern is the Z column. If you can, I'd suggest making it even more robust. The sturdier it is, the more it will resist vibration, so it will give a better surface finish.

Just my $0.02.

[underthetire]

Wow, too bad you weren't closer, we have an old Harrig surface grinder with magnetic chuck you could have had for cheap.

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[jalessi]

Where is the grinder located?

Wow, too bad you weren't closer, we have an old Harrig surface grinder with magnetic chuck you could have had for cheap.

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[Hezz]

More updates - things are moving along, although they are taking longer than expected. I'll try to post more updates soon

Good luck with this project. I find it interesting and I hope that you are able to obtain the tolerances you need with it. You can always fill the z column with rebar and EG and add additional external bracing to make it stiffer and more vibration resistant if you need to. I think that one of the greatest challenges will be to build an good low vibration spindle bearing for the grinding wheel and make it low enough in mass so that the vibrations are held in check by the Z column structure. Although mounting an inexpensive portable hand grinder is an option, I doubt that you will be able to get very good surface finish with that approach. If that is what is needed. Air bearings would probably be ideal for the grinding spindle if you have access to a lathe that can do pretty close tolerance work.

[Roadsidejobshop]

Hey DSpeck, all types of currency are accepted, even canadian 2 cent coins

- I am planning on putting a pretty well sealed accordion types bellows on top (since I'm planning on using flood coolant). Coolant filter-separator I am going to buy off-the-shelf(reasonably priced).
- the whole z-axis looked much much better in the model, not so good in real life. I'm planning on building a replacement z-axis tower assembly in the near future, but I will use the current version to make sure the machine works.The z-columns is pretty heavy though - about 25-30 kilograms and it will be filled with epoxy granite later on(so closer on 50kg for the column itself alone).

The whole assembly weighs about 120 kilograms and while filling it with epoxy granite will increase the weight to almost 200kg, it's still pretty light. But I also watch a lot of guys on youtube who have huge heavy machines, yet take 1 thousands deep cuts per pass. I find it really strange that machines that handle easily 10-15 thou per pass are being so underused

[Roadsidejobshop]

I've currently spent less than 50 euros on the whole machine build ... being poor is not nice LOL. I find that building this machine is teaching me a lot of important things about machine design, parts selection etc. Also, since I'm moving back to my home country in about 4-5 months, I have to keep the machines in a manageable size - no 2 tonne machines allowed

[Roadsidejobshop]

Alright, some updates: the original frame was too difficult to work with and after running through simulations I decided to build a completely new machine frame for the surface grinder (which should be much easier to set up after mounting rails). The original frame will be repurposed as a small CNC mill frame, used to mill my aluminium pieces. So I'm including many many pictures here and a few videos as well. I'll do a more in-depth video in a few days.

[Roadsidejobshop]

Alright, another update. As mentioned before, I decided to completely re-work the base frame to make sure I minimize the amount of deflection. I did some testing with the 3D model and the new version is much much stiffer - basically when the old version of the frame had 150kg (500newtons up, inward and to the right) applied, the deflection was around 0.02 ot 0.03mm. With the new design I applied 1000newtons in each direction and got a deflection(300kg total) and got a deflection of around 0.007mm (7 thousands of a millimeter, so roughly 3 tenths of an inch). I realise that ideals models are exactly that - ideal. But I believe that this version is much stiffer and also easier to set up.

Anyways, enough blabbering, here is the video:

[clmenz]

Very Interesting build/>> yeahhh (re)build!! I like seeing you re-analyzing the original model > > good engineering!!

1. Could you share a picture or three of the stress analysis/re- unianalysis of the models? Also really good to confirm where major stress points and magnitudes of rise of stress to guide possible critical areas/points of reinforcement..

2. Did you consider doubling the length of 11 mm right angle rods and drilling straight through, coupling the top tube loads more closely with the
bottom tube or does this create unwanted areas of weakness when they are welded. ?.

3. Although possibly expensive, did you heat stress relieve your welds prior to epoxy granite backfill?

4. In my tentative designs with epoxy granite, I am thinking of putting 4 3/4" to 1 " threaded rods in 2 very long very narrow' near intersecting "x's" down the tube that would be bolted into each end of the crossplates. Then back fill tubes with E.G. These tubes could then be compression loaded post E.G. cure . The compression loaded E.G. could also possibly increase the dampening of the tube. Haven't been able to figure out/model if compression loading might increase the strength of the tube beam in certain modes.
Chuck

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[clmenz]

The threaded rod also has more surface area to better mate with the E.G.
Alternatively, a ? cheaper but maybe not as strong alternative would be using 4 rebars : same narrow " x' s " configuration x2 #4 to #8 rebar could be cut and each end tapped to allow the tapped ends to compression load the end plates.
Chuck

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[Roadsidejobshop]

Clmenz - many good points and I'll try to answer them here:

1) I'll try to get access to the studies again, but I don't have a Solidworks licence so I have access at my local technical college once per week.
2) I did concider it, but in the model it did not seem to affect the overall stiffness very much, so i decided against it(as I am on a time crunch).
3) I also considered stress relieving the "raw castings", but in the end after maching the 2 large frames and having to remount them after a week to change the location of some holes, the castings had not moved at all, or less than 0.01mm (4 tenths of an inch). I would consider that relatively okay. The headstock piece moved after all the machining was done, but it was 0.02mm over about 170mm (and I am not sure if it was the maching marks or not, so I will stone the surfaces again). Stress relieving in Brussels is very very (too) expensive and putting the thing in a barbeque pit for 8 hours seemed like a great way to distort the whole thing.
4) compression loading is something I considered, but after consulting with a contact who did his thesis on vibration dampening machine frames, he said that it would be easier just to make caps for the tubes and use an expansion compound with the epoxy (and thats what I am going to do).

I should have a video coming up this week, the frame is machined (headstock needs one more hole) and after that I'll mount all the linear rails, screw supports, screws and decided the locations for the motors and drag-chains.

[Roadsidejobshop]

More pictures - prepare your enthusiasm! I assembled the frame and linear rails and such and it seems to be very very strong. After most of the parts were on the frame, I could not lift the machine even with an extra person. Nifty!

[Roadsidejobshop]

Made an update video on the progress so far. Should be up and working next week, either thursday or friday.

[Hezz]

Thanks for the video Roadside, it was enjoyable to watch.

[Roadsidejobshop]

Things are moving along nicely - the frames are painted, base frame is painted, I'm starting the re-assembly on tuesday or wednesday and hope to have the machine axis working by the end of the week! Just one picture for today - I'll add more soon.