Cutting slot in 20mm Steel Rod

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sams93

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I am making a fence for my newly restored planer thicknesser.

As part of this I need to cut 2 slots exactly 3mm wide by 20mm in depth into a 20mm round bright steel bar. I also need to drill a single 8mm hole through the centre.

I have attached sketchup renders of what I need to do.

I have barely any experience working with metals, and I am hoping for some advice on how to do it. Thoughts so far on options:

  • I have a very small woodworking bandsaw, but as I understand it will be far too fast to cut steel.
  • I have a dremel multitool - I was thinking I could work at it very slowly with some metal cutting discs and then use a small file to finish off to get it to dimension. I'm a bit concerned about how accurate the slots would be using this method.
  • I don't own an angle grinder and I'm not convinced it would be accurate enough to use for this purpose.
  • I have a hacksaw but again I am concerned about the accuracy.
  • I have a jigsaw and could use a metal cutting blade. I have seen an example of someone mounting the jigsaw upside down in a 'jigsaw table' configuration. I think I might be able to feed the bar into the blade fairly accurately using this method. (Photo attached)
Thanks!
 

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That's a job for a milling machine with a slitting saw of appropriate thickness.

I don't know if I have a slitting saw that's exactly 3mm thick, but I could certainly do that milling. How long is the 20mm rod?
 
I've made a few metal things lately with very limited metal working tools. I think trying to cut those slots with the tools you have and achieving some degree of accuracy would be very difficult. Can you adjust the design so that you only need flat faces on the outside of the bar?
 
I hate to be a Debbie Downer, but nearly everything you wrote in your first post indicates to me that you should take a dimensioned drawing of what you want to a machine shop and pay a professional to make the part for you.

I moved your thread to the General Metalworking forum.
 
That's a job for a milling machine with a slitting saw of appropriate thickness.

I don't know if I have a slitting saw that's exactly 3mm thick, but I could certainly do that milling. How long is the 20mm rod?
Rod is 330mm long. If this is something you might be able to help out and do then I could potentially post it up to you?


Frustratingly I was in yorkshire only 4 days ago!!
 
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I hate to be a Debbie Downer, but nearly everything you wrote in your first post indicates to me that you should take a dimensioned drawing of what you want to a machine shop and pay a professional to make the part for you.

I moved your thread to the General Metalworking forum.
I completely agree that this would be ideal. I have done this for the rest of the fence but I was hoping these slots and a single hole I might be able to come up with a solution for.

I am sadly a student at 29 so money isn't particularly forthcoming at the moment! I try and save where I can!
 
I presume you've got plenty of length to play with, fail and try again, no big deal.

I also presume those flappy bits are going to be housed in some way or another,
otherwise being mild steel would bend...like some of my f clamps with pivoting tommy bars do.

The interesting part will be sourcing a progression of files, that can take over once
after the junior, possibly bit of scraping with that before senior, scraping with the latter again,
and then some file or another, and a succession of those possibly.
Too narrow for a slimmer than usual (I've got three differing thickness) farmers own's,
though you might find something used which would be narrower, I reckon the same length won't be found, so will likely come down to short'uns which I haven't seen.
(looked for them, as I do this kinda thing occasionally)

Best I've seen without scouring the net are rather pants in regards to being nice, i.e flat, and teeth which cut everywhere,
so it might be a carpy cheapo set from the poundshop and draw filing it down the length.
Trouble is in the marking out I reckon, then it's just a bit of finger sweat.

Needle files which can flex to keep hollowing the middle out, not to obliterate the lines will be important.

Would be lovely to have a few files for the job, then one could possibly rig up a block.
Ain't nuthfin like a broaching fit from a good sized file.

But as mentioned, seems more sensible if a redesign to something more skookum
would be my preference also, if possible that is.

Tom
 
I completely agree that this would be ideal.

Ignore Debbie. She has no imagination.

As a woodworker, can you make a cube of wood to a reasonable degree of accuracy? Let us say 50mm to a side for the sake of putting a number on it.

Can you drill a 20mm dia. hole centrally on one face, square to that face and to a known depth?

Can you drill an 8mm dia. hole centrally on one of the other faces of the cube?

Make the cube, drill the two holes, glue your metal bar into the 20mm dia. hole. Use the 8mm dia. hole as a guide for the drill bit to put the hole in the metal rod.

If your metal rod was a wooden dowel that needed the same features in it, how would you do it? I would use a table saw setting the fence so the edge of the blade coincides with the edge of one of the slots. Make one cut then adjust the fence until the slot is the correct width.

As the two slots are symmetrical about the rod centreline, rotate the rod 180 degrees and do each cut twice, once for each slot.

How do you ensure exactly 180 degrees of rotation? Well, if your rod were enclosed in something like a 50mm cube, it is easy. That also has the benefit that the slots are parallel with the 8mm hole.

Buy a cheap grinder, some 1mm slitting discs and make a jig for it. It wants to look just like a table saw, with the grinder blade in the same place as the saw blade would be. Make a fence, identical to that used on a table saw. For the slot cutting, I would have the rod vertically, so the highest point of the grinding wheel sets the depth. Use packers under the enclosing cube so alter the depth. A packer could be a thick sheet of paper. A similar packer could be used against the fence to finesse the slot width.

It may be wise to pre-cut slots in the wooden cube or it will smoke a bit the first time the grinder sees it.
 
This could be an opportunity to try this bodgery, (just mentioning for fun, timestamped vid of some thin disc dado stacking on a grinder.)
Sorry I found that very ingenious, never would'a thunk it, well without the need at least,
would'a been a sweet&sour thing to have seen after doing something much more difficult.


Ye probs won't click, and annoyingly I couldn't find this on me computer,more importantly nor in the search bar, even though I've posted it here more than once, so will try again and post
(excuse the shouting) MATT CREMONA'S DADO GRINDING TIP
Matt Cremona's dado grinding..png



I'll bet Bosch or someone make various thickness slitting discs, often marketed for stainless,
bit of trial and error with some scrap first, the cheapie 1mm discs might be worth experimenting with, due to a bit of wobble, not to mention deflection.
Would likely need to make a holster for the grinder which can thread in either side,
which would match your work height,
and a track of sorts, say like you would use stops clamped down for routing a mortice without guide bushing.
Likely need to draw file the last wee bit, no bothers.

Interesting conundrum, thanks for posting.
:)
Tom
 
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Rod is 330mm long. If this is something you might be able to help out and do then I could potentially post it up to you?


Frustratingly I was in yorkshire only 4 days ago!!
Sure. 330mm is definitely postable.

Given that the rod is 20mm in diameter, and the slots need to be 3mm wide, I'd just need to know the width of the central part (marked 'a' in the image below) and the distance of the centre of the hole to the end of the rod (marked 'b').

It looks as though the hole is counterbored - so the bore diameter and depth would be important too. EDIT: Looking again at the other images; it appears to just be an 8mm hole straight through; just that angle makes it look counterbored. So that's easier.
 

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Got any friends that are good welders? Flat bar could be welded or brazed to the end of the 20mm rod, then drilled and lastly made round with a few files and sandpaper. You could also do it by cutting the round stock to have just the flat centre and then weld on the two cheeks.

Pete
 
Sure. 330mm is definitely postable.

Given that the rod is 20mm in diameter, and the slots need to be 3mm wide, I'd just need to know the width of the central part (marked 'a' in the image below) and the distance of the centre of the hole to the end of the rod (marked 'b').

It looks as though the hole is counterbored - so the bore diameter and depth would be important too. EDIT: Looking again at the other images; it appears to just be an 8mm hole straight through; just that angle makes it look counterbored. So that's easier.
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In your diagram:
A = 6mm
B = 11mm
 
Could you not make a jig which holds the bar and feeds it into a static mounted angle grinder with a 3 mm blade on it.

Perhaps a couple of 4x2 timbers with a 20mm hole drilled in it. Which run on a alu track towards the fixed angle grinder?

Just a thought?
 
That looks feasible. I checked my slitting saws and the only issue might be the 20mm depth of the cut; most of them will only cut up to around 15mm deep (a combination of the blade diameter and space required for the saw arbor). I have a couple that are larger, but they're not 3mm thick so it would have to be done in stages and hope it doesn't deflect.
 
likes of the big grinders 7" and 9" use thicker cutting discs than 4-4.5 and 5".which have between .80-1mm and sub 2mm only discs i know that will cut 3mm in one pass are the diamond/Tungsten carbide ones.
Unless bar is solidly clamped in a decent vice trying to work a grinder is more akin winning the lottery if want cuts in right place and your pinkies still attached to hands!.

One thing that would work is a metal cut off saw and a pillar drill vice as needs to hold lower than a normal vice and rigid draw cuts on bar then cut in with saw then stop and revolve bar as cuts just like with a circular saw will be short on under side.
As i said bar will have to be held solid as cutting to one side on centre.
once done finish with larger flat files ie wide as cuts stays in line.

If was local could have cut end off bar cut and drilled then weld back together.
Have a tungsten carbide cut off saw plus 5 and 9" grinders.

Best way i'd say is find engineering places around your way or Fabricators/places that weld or repair likes of large implements like tractors/machinery have a friendly word in there lughole explain/show what our aims are and often will say bring it in we'll have a look and many will be happy to help and nominal amount to do it or free and offer them some cash as always helps to grease palms!.

Milling machines will do job well
 
If you can’t get the rod machined have you looked at say a go pro mount and then attach that to a bar with a threaded hole , not sure on strength though but may work
 

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Could you not make a jig which holds the bar and feeds it into a static mounted angle grinder with a 3 mm blade on it.

The difficulty with using a 3mm blade is that you get one chance at the cut. If there is any run out on the disk (angle grinder disks are not precision instruments), it will cut wider than nominal and the part will be ruined.

If you use a standard 1mm slitting disk, it is easier to control the cut as you are removing 1/3 of the material each pass. You can sneak up on the correct width a little at a time, checking after each pass.

---

Another mad idea: 20mm rod is perfect to go through the hole in an MFT. Concrete the lower end into the floor, put the MFT over the rod and cut the slot with a tracksaw and a very well dialed-in parallel guide. You could use a long piece of 8mm rod through the hole and a good square to align the track perpendicular to the hole.

Edit:

One of these would make the grinder look a little like a track saw and can be mechanically guided in a straight line:

https://www.amazon.co.uk/Bascet-Grinder-Bracket-45°Adjustable-Machine/dp/B0B51BW6N6/
 
My background is in mechanical engineering design (retired and now a very amateur woodworker.)
I know it seems obvious to exactly replace what was there but often a redesign improves things.
Go back a step.
For this I would be asking first why the two components have a yoke and how essential is that the joint resists twisting while still freely pivoting? What forces are likely? Can you shim a wider toleranced gap to get your required lateral play.
Secondly while your time may be free, sometimes buying in ready made components is still worth it.
For example, threading the rod and screwing on a type of ball joint which are available at suitable sizes , say M8 internal thread, might be part of a solution. Typically EBay at about £2 each.
Finally from bitter experience filing flat and square is harder than it looks ( based on making a test piece consisting of a 1" thick dovetail joint - hacksawed and filed out of 2" black mild steel bar when training). But you all already know that using hand tools well takes practice.
Sorry this isn't a specific solution, someone on the metalworking forum may know exactly the best way from their experience. But good luck with getting the job working.
 
If I had to do this without a mill I'd file the top square

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And then drill a series of 3mm holes.

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Then finish with a file.

DO NOT be tempted to overlap the holes. It won't work.

The drill will pull into the existing hole and then you'll need to start a new hole and you'll be left with a lot more to clean up.


Realistically you NEED at least a bench drill and for preference a proper drill press.

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If you don't already have a bench drill you will have to get one at some point so now's the time.

You might get one for £20 second hand off Gumtree or some other local advertising.

1677229536468.png



At a push you might get away with a drill stand (about £20).

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