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Thread: Tapping large holes

  1. #1
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    Tapping large holes

    I am making 4 wheel adapters out of 3/4" mild steel plate that need 10 holes drilled and tapped for 1" bolts. The 1" is just to match the holes in the wheels and not a requirement for a strength. I can drill the holes no problem but wondering how hard it would be to hand tap 40 1" holes? The shop that will cut the adapters on a CNC plasma wants $200 per adapter to drill and tap the holes which is too expensive. The cost to cut the adapters is $250 each. The outer holes can be cut with the plasma but plasma leaves too hard of an edge for tapping is why they have to be drilled. I don't think it should cost almost as much to tap the holes as the adapters cost. I think 40 1" holes would be too much of a chore especially considering I'm not supposed to exert myself too much but maybe they wouldn't be too hard if I made some kind of jig? The holes would have to be straight.

  2. #2
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    Re: Tapping large holes

    Get a good gun tap in your size, use a mag drill with some Trefolex and let her rip. That's what I do.

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    Re: Tapping large holes

    I agree
    I have taped thousands with a mag drill.
    If brake a big tap just use mig or stick and weld straight down up to nut. Do not touch the side of the tap hole.

    Dave

    Quote Originally Posted by Woznme View Post
    Get a good gun tap in your size, use a mag drill with some Trefolex and let her rip. That's what I do.

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    Re: Tapping large holes

    Have them add just a "drill point" to the file. It just fires the torch to make a "punch" mark to where you are going to drill and tap the holes. Then get a carbided drill yourself to drill the hole, then tap. The spot it makes is not that bad to drill. I have done something like this before.
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    Re: Tapping large holes

    Takes a lot of torque to tap 1." I doubt my Jacobs 1" super chuck could even grip a 1" tap tight enough to keep it from spinning.

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    Re: Tapping large holes

    Unless they have a way to machine-tap the holes, I can see them charging that much since it'll take a person doing the work. Maybe they don't feel comfortable doing it because they worry about tolerances?

    Either way, I'd have them cut the holes for you since they're already there and cutting the steel. Have them cut 5/8" or 3/4" holes so you can open them up to tap size with your own drill. That'll speed things up considerably on your end.

    As for tapping them by hand, it's hard work for sure, but doable. Plus it's an excuse to buy a nice vintage Greenfield tap wrench in one of the bigger sizes. I'm always looking for an excuse....

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    Re: Tapping large holes

    Quote Originally Posted by lars66 View Post
    Takes a lot of torque to tap 1." I doubt my Jacobs 1" super chuck could even grip a 1" tap tight enough to keep it from spinning.
    Just start it to get it straight and then finish by hand with a tap wrench. This is what I do on my Bpt. Mill. Start it in back gear and hit the switch off after it starts a few threads straight. Then finish off by hand.
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    Re: Tapping large holes

    Quote Originally Posted by VaughnT View Post
    Unless they have a way to machine-tap the holes, I can see them charging that much since it'll take a person doing the work. Maybe they don't feel comfortable doing it because they worry about tolerances?

    Either way, I'd have them cut the holes for you since they're already there and cutting the steel. Have them cut 5/8" or 3/4" holes so you can open them up to tap size with your own drill. That'll speed things up considerably on your end.

    As for tapping them by hand, it's hard work for sure, but doable. Plus it's an excuse to buy a nice vintage Greenfield tap wrench in one of the bigger sizes. I'm always looking for an excuse....
    Not with plasma. If you cut the holes to smaller size and try to open them up with a drill for you tap size you will have issues and it will not be straight. Tools will break. Been there done this. Have them do a peck pierce. A peck pierce is not pierced all the way through. It is just a divot/punch mark and it is not really hardened due to a short burst/blip from the torch.
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    Re: Tapping large holes

    I got a quote from a machine shop which I think is a great price... $88/adapter for a total of $352 to drill and tap 40 1"-8 holes. $8.80 per hole is not worth the frustration of trying to do it myself. I know a machinist that could do do it in a vertical mill, but would be a bit of pain because of the size, who agreed $352.00 is a good price to do the holes. Now I can proceed with my project. It's one of those things that think you can do in your mind but when you actually go to do it, is a lot harder than you thought it would be.

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    Re: Tapping large holes

    Quote Originally Posted by Welder Dave View Post
    I got a quote from a machine shop which I think is a great price... $88/adapter for a total of $352 to drill and tap 40 1"-8 holes. $8.80 per hole is not worth the frustration of trying to do it myself. I know a machinist that could do do it in a vertical mill, but would be a bit of pain because of the size, who agreed $352.00 is a good price to do the holes. Now I can proceed with my project. It's one of those things that think you can do in your mind but when you actually go to do it, is a lot harder than you thought it would be.

    That's the ticket right there. I've done a quite a few 1"ers in my time. Doing a few are a pain in the *** but 40, That's just flirting with disaster. Could of easily cost you twice that said and done. Doing this for a living we always have to take liability into account. Lot less stress going this route and by going this route it frees you up to get ahead on other aspects of your project.
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    Re: Tapping large holes

    if it was just a snap of the finger and lose $350, and everthing would be right, it would sound appealing. but its the hassle of deliver/pickup , chance of it not ur expectations/tolerances, etc. i hate to rely on someone else. i usually pass on job, rather than farm something out. id find a cheap 12 point socket or something to fit the taps end, weld a big bar to the socket, and have a nice tap wrench. countersink them holes, put a spring tap guide under chuck for starts, get generous w/ some castrol moly dee, and it should be a cakewalk, as long as u get the tap started straight. if u did 6 a day, in a week u'd have it done w/ an extra 300 saved. however u know ur situation better than i do
    Last edited by 123weld; 4 Weeks Ago at 09:41 PM.

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    Re: Tapping large holes

    I just used chuck on the B&D mag drill.
    I used up to 7/8" tap.
    If tap slip it is time for a new tap.
    If push a tap you need to remove a broken tap ( not fun )
    If need a tap adapter just use a square socket and a modified extension to the drill chuck a tab on the extension will stop rotation in chuck.

    Dave

    Quote Originally Posted by Freebirdwelds View Post
    That's the ticket right there. I've done a quite a few 1"ers in my time. Doing a few are a pain in the *** but 40, That's just flirting with disaster. Could of easily cost you twice that said and done. Doing this for a living we always have to take liability into account. Lot less stress going this route and by going this route it frees you up to get ahead on other aspects of your project.

  17. #13
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    Re: Tapping large holes

    The problem with plasma cut holes is that they have a hard edge that would ruin a tap and likely a drill bit as well. Otherwise I'd have the holes cut with the plasma. The outer holes will be cut with the plasma as they don't need to be tapped.
    I think an experienced machine shop could do a lot better job than I could. The adapters are for my own use. To do myself I'd have to buy a good tap and drill bit that would be over $200. Being the holes are for mounting a wheel, they have to be dead straight. If I had to rent a mag drill would be at least $80 and what if I broke a tap or got a hole crooked? I suppose I could weld up a bad hole but that's a hassle too. The bolt pattern has to be fairly exact as there's a cut out in the adapters to clear the valve stem guard on the new wheels. The existing hubs also have a bolt missing as it leaves room around the valve stem. These are 1 off adapters I'm designing as I doubt anyone else would be in the same predicament. I got brand new tires with wheels but the tires are urethane filled for a telehandler so can't be removed from the rims without destroying them. The tires alone are worth about $1600US and the HD rims I'd imagine are around $1000. I got them for $2500Cad. plus 10% buyers premium for a total of $2750. The adapters will cost about $375.00 each to make. I'll be ahead of the game and never have to worry about air pressure or flats. I don't know if anybody has ever ran foam filled tires on a grader but if they work on telehandlers and front end loaders, I can't see why they wouldn't work on a grader. Might not have quite as much traction but I'm not going to be working in mud and trying to push the machine to its limits.
    Last edited by Welder Dave; 4 Weeks Ago at 01:32 AM.

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    Re: Tapping large holes

    I may have some even better news. I took my little bit of a crude template to the shop that is tapping the holes and the guy there was super nice. He thought $200+ to cut the adapters seemed high so asked if I could leave my template with him. He said he regularly deals with a few shops that have plasma, water jet and other types of cutting when they need larger parts cut. He said shops that do a lot of cutting usually have common sizes of plate in stock and therefore could likely give a better price. He hadn't heard of the other shop I initially talked to. Would be great if I could get $120 or more off the cost. It all adds up. $120 would pay for all the fasteners. The shop is 10 minutes away from me too while the other shop is way on the other side of the city about 40 minutes away.

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    Re: Tapping large holes

    https://www.ebay.com/itm/26472497785...gAAOSwLhJetbPe

    https://www.ebay.com/itm/16473208430...4AAOSwJVxgPFG4

    Depending on your class of fit, a hole can be drilled to be loose, or tight. This affects tapping effort.

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    Re: Tapping large holes

    Looked at Machinery's. Loosest fit corresponds to 59/64 drill bit.

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    Re: Tapping large holes

    The drill size I use for A36 tapper tap 70% thread size. Most thread charts use 65% to 70%. But soft aluminum you want 80% thread and harder steel 60% to 65% thread.
    Using a Mag drill use a tapper first.

    Dave

    Quote Originally Posted by farmersammm View Post
    Looked at Machinery's. Loosest fit corresponds to 59/64 drill bit.

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    Re: Tapping large holes

    7/8" hole gives 77% thread. I'm sure an experienced machine shop that has been around for a long time has no problem tapping holes correctly. I wouldn't trust a $15 tap to do 40 holes in 3/4" plate and being 1" requires some serious torque to be doing by hand. I also wouldn't want to buy 2 or more taps. A Cle-Line (Greenfield) tap is about $75 and Dormer about $140. I'd need a large tap handle for at least $60 and then about $40 for a good quality drill bit and around $80 to rent a mag drill for a day. I wouldn't save any money and it's just not worth the hassle. If even 1 hole gets screwed up, I'd have to weld it up and start over. The plates will be fairly heavy too to be moving around. I don't want to injure my back after having the compression fractures repaired with bone cement. Supposed to be stronger than healthy bone but I'm not going to be the guinea pig to test that theory. I currently have muscle aches in my back because the muscles have to get back to being used a lot more frequently. It's very important I keep active so I don't end partially handicapped from just lying around doing nothing. Even slight bending can make my back ache more if it's an awkward position. Appreciate the advice and think I have found the best solution to make the adapters.
    Last edited by Welder Dave; 4 Weeks Ago at 01:47 PM.

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