Drilling mild steel

[Bruce Mack]

I have an exercycle that I still use occasionally after 20 years, more so recently to strengthen my spindly legs. I find the wide seat uncomfortable and want to replace it with a bicycle seat which though narrower is better suited to my anatomy. As the seat height adjustor is topped with a 1/8" plate welded to it I have to adapt it to a bicycle seat post by drilling an appropriate sized hole, approximately 25.4 mm-28 mm in diameter. The bicycle seat tube topped with the bike saddle can then be adjusted in height using the exercycle seat height adjustor. Drilling was difficult. Though I hoped to complete it with a step drill bit, my progress to just 3/8" using a hand held power drill with a twist bit has been slow (1/8-1/4-3/8 so far) and the bit has bound several times. I am certain I can't get far with the step bit which I am trying to cancel from Amazon and which I should not have ordered before my test drilling.
I have only a woodworkers' drill press, no drill press vise, and no way of securing the relatively heavy seat height adjustor to the drill press table. I am reconciled to the present seat but if someone has a pertinent suggestion I would be delighted. The bloody knuckle occurred from a scrape not related to the drilling but I included it as click-bait.
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[Lee Schierer]

I also, on occasion, drill holes in metal on my wood working drill press. I see the wound on your finger where the piece of metal bit you.

Your first step should be to secure the piece you are drilling such that when it grabs you hands are not struck by the rotating piece. Use either a drill vice or mount the metal piece on a board that can be clamped to your drill press table. Set your depth stop so you cannot drill all the way through the piece of wood.

Once the piece is securely held. Make sure your drill bits are sharp. Add a bit of lubrication to your drill bit and make sure your drill bit is turning about 450 rpm. Use light but steady downward pressure to achieve consistent chip removal as you drill into the piece. You may want to take smaller incremental steps as your hole gets larger in diameter.

[Richard Coers]

Step drills actually work quite well. The geometry is different and you don't get the grabbing you can get with a twist drill. That is not a recommendation to not secure the metal in a vise! Your hole size statement is a bit unsettling. A range of 1/8" is quite large. I'm trying to decide you think you can just put in a large drill bit and do that in one setup. A much better technique is to start with a 1/4" drill bit and then change to larger as you progress. One setup would be extremely difficult to do. You should move this to the metalworking sub forum, not woodworking.

[Tom M King]

If a 1" hole will work, send it to me and I'll drill it on a drill press I have set up for metal. I only have fractional bits that large, but 1" equals 25.4 mm. It's an easy job for someone set up for it. I'll get it right back to you.

[Bill Dufour]

I would use woodscrews or nuts and bolts with washers through the holes and screw the workpiece onto a piece of scrap 2x4. Then brace the long end of the 2x4 against the left side of the support coluum. I would c-clamp the assembly to the dp table so it does not lift up. Since I have one I would use a big countersink or tapered reamer to enlarge the hole.
Even if you had a vise, drilling a 1" hole might spin the vise unless it is clamped down so it can not spin.
Bill D

[Tom M King]

I forgot I have car reamers too, but I'll have to check to see if I have any over 1".

[Cameron Wood]

Drilling a large, precision hole in that plate seems like a bad idea. Even if you got it the right size for a seat post, how would that be held in place?

Can you post pics of the machine?

[Bruce Mack]

Drilling a large, precision hole in that plate seems like a bad idea. Even if you got it the right size for a seat post, how would that be held in place?

Can you post pics of the machine?
The post is 24" long and the plate is welded to it. It is heavy and built solidly. I held it securely in a machinist vise bolted to the top of my workbench and drilled it without anything moving beside the drill when it caught. The seat posts can be purchased in many diameters 25.4, 27.5, 28.6, 30.9, 31.6 mm. The hole I drill will be a few mm. larger than the post. Amazon sells tubular shims that can be of varied thickness, for instance a tube of 27.2 mm diameter can be matched to a 28.6, 30.0, 30.9, or 33.9 mm. O.D. sleeve. I intend to have it fit snugly but not perfectly as the tubes are 350 mm. long and my weight will hold it in place with the sleeve chosen to minimize lateral shift. Obviously you would want a clamping mechanism for street bicycling.

My knuckle truly was injured when I slammed it against a drill bit after it was chucked, but not during any machining process.
Thanks to Tom's offer and others' suggestions. My cancellation of the step drill bit came too late so I may try it at 1 1/8" (28.6 mm.)

[Maurice Mcmurry]

A bi-metal hole saw could still be used. You could drill through a piece of wood, bolt that to the seat base as a guide and proceed with caution, it may be some funky imported steel. It will be an epic hack when you get it done. A Good wash, Neosporin, and a bandaid for that wound : (

[Bruce Mack]

A bi-metal hole saw could still be used. You could drill through a piece of wood, bolt that to the seat base as a guide and proceed with caution, it may be some funky imported steel. It will be an epic hack when you get it done. A Good wash, Neosporin, and a bandaid for that wound : (
Thank you, Maurice. I like this option. I'm too dumb to stop yet and too weak to move a new exercycle to the second floor where the old one resides.

[Tom M King]

It's not safe to drill a hole that large in metal that thick by hand. I tried enlarging a hole in a tractor block with a 3/4" spade handle drill using a 49/64" bit. We had a 5' long 3/4" pipe with a 300 lb. very strong helper holding the end of the 5' handle. The bit caught, and it bent the bit. No one got hurt, but that was my last try at that, and I bought a magnetic drill press for the job.

Even with a big spade handled drill, there is too much danger of injury. I would think about welding another type of seat mount on the top of that post, even if you needed to cut that plate off. I would probably modify it to use a regular seat post by cutting part of the top of the square tube and welding in a couple of bushings, then welding it back on. It's not a hard job for someone set up to do that sort of thing.

[Cameron Wood]

Thanks for the pics.

Doesn't the saddle that you want to replace have rails the same as the new saddle?

Alternatively, cut off the overhanging part of the plate and weld on a round seatpost.

[Bill Dufour]

Can you bolt a floor flange to that plate and use a piece of water pipe as a seat post.
Bill D

[David Buchhauser]

I have an exercycle that I still use occasionally after 20 years, more so recently to strengthen my spindly legs. I find the wide seat uncomfortable and want to replace it with a bicycle seat which though narrower is better suited to my anatomy. As the seat height adjustor is topped with a 1/8" plate welded to it I have to adapt it to a bicycle seat post by drilling an appropriate sized hole, approximately 25.4 mm-28 mm in diameter. The bicycle seat tube topped with the bike saddle can then be adjusted in height using the exercycle seat height adjustor. Drilling was difficult. Though I hoped to complete it with a step drill bit, my progress to just 3/8" using a hand held power drill with a twist bit has been slow (1/8-1/4-3/8 so far) and the bit has bound several times. I am certain I can't get far with the step bit which I am trying to cancel from Amazon and which I should not have ordered before my test drilling.
I have only a woodworkers' drill press, no drill press vise, and no way of securing the relatively heavy seat height adjustor to the drill press table. I am reconciled to the present seat but if someone has a pertinent suggestion I would be delighted. The bloody knuckle occurred from a scrape not related to the drilling but I included it as click-bait.
492918


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I would recommend using a large C-clamp to clamp your plate to your drill press table. If you don't have any, then this is a good time to buy some. Use a piece of scrap plywood between your metal and the table to prevent drilling into the table. Use the slowest speed your drill press offers. If you need a 1" dia. hole, then a hole saw designed for metal will work if you size the pilot hole in your part to match the hole saw pilot bit (normally 1/4" diameter). If you have already drilled the pilot hole larger than 1/4", then you could try using the hole saw (in the drill press) with no pilot. Make sure your part is securely clamped - use several large C-clamps - not wood working clamps - and crank it down tight. Use plenty of lubricating oil on the hole saw as you slowly proceed to create the hole.

Here in my shop, I would clamp that part to the milling machine table and use a hole saw mounted to the spindle.

Good Luck!

David

[Maurice Mcmurry]

I recommend a drill with a clutch. I have two drills that have a clutch. A little Ryobi corded Diver drill and a big D handle DeWalt SDS with an adaptor and chuck. The clutch is a great safety feature.

[Ole Anderson]

Chuck a 1" bi-metal hole saw with a centering bit into your DP. Set RPM at your lowest available. Push your fence up against a flat side of the work to keep it from spinning, lube/cool the bit with oil.

[Ronald Blue]

The hole saw is going to be the most workable solution for you. In a drill press. Hopefully your drill press has a table that will adjust to 90 degrees and attach post to it with clamps. I encountered these hole saws last summer and while more expensive upfront are they ever a delight to use. Between the hex on the drill bit to prevent slipping to the quick change feature they are awesome. This is a link to the mandrel with a 3/8" bit so it would work well with the current hole you already have.

I would look into putting a cross bolt in the base of the seat post once you get the hole bored. Just my .02 cents there.

This is a link for the Diablo arbor but it gets you headed down the path. These should be available locally.

https://www.amazon.com/s?k=diablo+holesaw+arbor&i=tools&crid=29LF9UDA928ZP&sprefix=diablo+holesaw+arbor%2Ctools%2C207&ref=nb_sb_noss_1

[Maurice Mcmurry]

The post is 24" long and the plate is welded to it. It is heavy and built solidly. (28.6 mm.)

Those images help. I have welding as an option so my approach to that would be to cut the plate off of the square tubing and weld the seat tube from a junk bike inside with a series of spot welds through some small holes.

[Floyd Mah]

You are getting a lot of advice on how to wrangle a large drill into a difficult to clamp post. I wouldn't try any of those solutions.
All you need to do is drill into 1/8" steel. That's very easy. Just mark the desired opening into the steel plate. Use a punch to mark positions inside the circle and drill a series of holes. Knock out the waste metal and file down the opening with a round file. Files for sharpening chaiin saw blades would work well for this task. You can attach sandpaper to a round dowel or broom handle for the final smoothing. If you have access to a sanding drum of 3/4" diameter, use that. You would be surprised how quickly you can do this job. Years ago I made a large shoulder plane just using a drill to shape the sides. If you want to make the holes as close as possible, just drill two adjacent 1/8" holes in a metal bar, and use one hole as a pivot with a nail to guide positioning of the drill bit for the drilling of the second hole.

[John K Jordan]

It's not safe to drill a hole that large in metal that thick by hand….

It can result in horribly serious injury in a heart beat. If without the proper tools or experience maybe find someone to do it - as Tom suggested it seems like a simple task for many of us. Even lots of farmers are equipped for such things.

For example if I understand what’s wanted I might use the big drill press or even cut the hole with the plasma cutter (or maybe just start with a new piece of steel), grinding and welding as needed. There is likely someone within a few miles of anywhere who can safely modify or make a suitable mount in short order, even from scratch.

[Bruce Mack]

It can result in horribly serious injury in a heart beat. If without the proper tools or experience maybe find someone to do it - as Tom suggested it seems like a simple task for many of us. Even lots of farmers are equipped for such things.

For example if I understand what’s wanted I might use the big drill press or even cut the hole with the plasma cutter (or maybe just start with a new piece of steel), grinding and welding as needed. There is likely someone within a few miles of anywhere who can safely modify or make a suitable mount in short order, even from scratch.

I canceled the step drill as, from reading the replies and checking what I can find from other online sources, I see no enthusiasm for its use in steel of this thickness. I had considered a 1 1/8" carbide tooth hole saw but as I have already drilled a 3/8" hole in the seat adjuster top plate, it is no longer plausibly "safe" (the pilot bit is 1/4"). A handheld chainsaw file will be something to try.
I am grateful for the safety comments.

[Cameron Wood]

https://www.youtube.com/watch?v=grv0-YxQzwc

10:20

[Ronald Blue]

The simplest fix is to take the post you want to adapt in there and the post you have to a welding shop and have them cut a hole with a plasma cutter for the new post. It will barely discolor the paint. Then tack weld it in place.

[Tom Bussey]

I am a retired Tool and Die Maker who still works part time in a tool room. 1. I would use a drilling speed of about 250 RPM. That way you will not need coolant of any kind. Hopefully you have a fence. Move it close to your work it shouldn't touch it. Just let the part float so the drill point can center on the center punch mark. The fence will stop the rotation of the part The down ward pressure of the drill bit will keep the part flat on the table. I would put a piece of wood under the part because when the drill starts to come out the bottom you will be the primary burr. Drilling into and while drilling there is no cause for alarm. It is when the drill bit starts to come out the bottom. You will be able to feel the bit starting to come out. Lessen the drilling pressure From there on take your time and go slow.

[Bruce Mack]

I thank everyone for their suggestions and their cautions. I don’t know anyone who would drill the hole for me and I did not want to take the part to a machine shop.
I found a couple of YouTube videos showing the safe use of a handheld drill to drill thin mild steel. Yesterday I bought a bimetal 1 1/8" hole saw and a bronze bushing to reduce the hole I had previously drilled to the 1/4” size of the pilot bit. Today I used my old Ridgid NiCad drill with an accessory handle to resist any kickback. It weighs 5 pounds. I ran it at a low speed and used mineral oil in the channel I created. Everything went well. I do not post this as a gloat. Your warnings allowed me to take every precaution including wearing goggles. I will now order a bicycle seat post, shims, and saddle.

[John Kananis]

Glad it worked out for you. Does your drill press table not pivot to vertical?

[Bruce Mack]

Glad it worked out for you. Does your drill press table not pivot to vertical?
John, it does go to vertical. My photo of the seat adjustor with the drill press is misleading, meant to show the proportions of the workpiece and not an intended clamping arrangement. I will edit it out.
The clamping on my workbench was so secure and the drilling was so easy initially that I chose to continue with the hand-held.

[Bruce Mack]

The new seat is secure. The shim fits snugly and there is no movement of the post when I ride. I let the post bottom out with my weight and I adjusted the seat height using the exercycle adjuster. The first photo shows the collar of the shim with a segment of the seat tube above it.

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