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.
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.
NOW you tell me...
Contributor
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+ho...f=nb_sb_noss_1
Contributor
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.Originally Posted by Bruce Mack
Best Regards, Maurice
Member
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.
Moderator
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.
[OP]
Member
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.
Last edited by Bruce Mack; 01-08-2023 at 12:04 PM.
Contributor
Contributor
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.
Contributor
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.
Tom
[OP]
Member
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.
Last edited by Bruce Mack; 01-11-2023 at 6:35 PM. Reason: clarity
Contributor
Glad it worked out for you. Does your drill press table not pivot to vertical?
[OP]
Member
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.
[OP]
Member
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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